configure: use AC_LANG_PROGRAM consistently

Avoid warnings from Autoconf 2.68 about missing use of AC_LANG_PROGRAM
and friends.

Quoting autoconf-2.68/NEWS:

  ** The macros AC_PREPROC_IFELSE, AC_COMPILE_IFELSE, AC_LINK_IFELSE, and
     AC_RUN_IFELSE now warn if the first argument failed to use
     AC_LANG_SOURCE or AC_LANG_PROGRAM to generate the conftest file
     contents.  A new macro AC_LANG_DEFINES_PROVIDED exists if you have
     a compelling reason why you cannot use AC_LANG_SOURCE but must
     avoid the warning.

The underlying reason for that change is that AC_LANG_{SOURCE,PROGRAM}
take care to supply the previously computed set of #defines (and
include standard headers if so desired) for preprocessed languages
like C and C++.

In some cases, AC_LANG_PROGRAM is already used but not sufficiently
m4-quoted, so we just need to add another set of [quotes] to prevent
the autoconf warning from being triggered bogusly.  Quoting all
arguments (except when calling special macros that need to be expanded
before recursion) is better style, anyway.  These and more rules are
described in detail in 'info Autoconf "Programming in M4"'.

No change in the resulting config.mak.autogen after running
./configure intended.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

aclocal.m4

@@ -13,15 +13,15 @@ AC_DEFUN([TYPE_SOCKLEN_T],
          git_cv_socklen_t_equiv=
          for arg2 in "struct sockaddr" void; do
             for t in int size_t unsigned long "unsigned long"; do
-               AC_TRY_COMPILE([
+               AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
                   #include <sys/types.h>
                   #include <sys/socket.h>
 
                   int getpeername (int, $arg2 *, $t *);
                ],[
                   $t len;
                   getpeername(0,0,&len);
-               ],[
+               ])],[
                   git_cv_socklen_t_equiv="$t"
                   break 2
                ])

configure.ac

@@ -345,7 +345,7 @@ esac
 AC_CACHE_CHECK([if linker supports -R], git_cv_ld_dashr, [
    SAVE_LDFLAGS="${LDFLAGS}"
    LDFLAGS="${SAVE_LDFLAGS} -R /"
-   AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [git_cv_ld_dashr=yes], [git_cv_ld_dashr=no])
+   AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], [git_cv_ld_dashr=yes], [git_cv_ld_dashr=no])
    LDFLAGS="${SAVE_LDFLAGS}"
 ])
 if test "$git_cv_ld_dashr" = "yes"; then
@@ -354,7 +354,7 @@ else
    AC_CACHE_CHECK([if linker supports -Wl,-rpath,], git_cv_ld_wl_rpath, [
       SAVE_LDFLAGS="${LDFLAGS}"
       LDFLAGS="${SAVE_LDFLAGS} -Wl,-rpath,/"
-      AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [git_cv_ld_wl_rpath=yes], [git_cv_ld_wl_rpath=no])
+      AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], [git_cv_ld_wl_rpath=yes], [git_cv_ld_wl_rpath=no])
       LDFLAGS="${SAVE_LDFLAGS}"
    ])
    if test "$git_cv_ld_wl_rpath" = "yes"; then
@@ -363,7 +363,7 @@ else
       AC_CACHE_CHECK([if linker supports -rpath], git_cv_ld_rpath, [
          SAVE_LDFLAGS="${LDFLAGS}"
          LDFLAGS="${SAVE_LDFLAGS} -rpath /"
-         AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [git_cv_ld_rpath=yes], [git_cv_ld_rpath=no])
+         AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], [git_cv_ld_rpath=yes], [git_cv_ld_rpath=no])
          LDFLAGS="${SAVE_LDFLAGS}"
       ])
       if test "$git_cv_ld_rpath" = "yes"; then
@@ -472,15 +472,9 @@ if test -z "$NO_ICONV"; then
 
 GIT_STASH_FLAGS($ICONVDIR)
 
-AC_DEFUN([ICONVTEST_SRC], [
-#include <iconv.h>
-
-int main(void)
-{
-	iconv_open("", "");
-	return 0;
-}
-])
+AC_DEFUN([ICONVTEST_SRC],
+[AC_LANG_PROGRAM([#include <iconv.h>],
+ [iconv_open("", "");])])
 
 if test -n "$ICONVDIR"; then
    lib_order="-liconv -lc"
@@ -500,7 +494,7 @@ for l in $lib_order; do
     old_LIBS="$LIBS"
     LIBS="$LIBS $l"
     AC_MSG_CHECKING([for iconv in $l])
-    AC_LINK_IFELSE(ICONVTEST_SRC,
+    AC_LINK_IFELSE([ICONVTEST_SRC],
 	[AC_MSG_RESULT([yes])
 	NO_ICONV=
 	break],
@@ -528,18 +522,12 @@ fi
 GIT_STASH_FLAGS($ZLIB_PATH)
 
 AC_DEFUN([ZLIBTEST_SRC], [
-#include <zlib.h>
-
-int main(void)
-{
-	deflateBound(0, 0);
-	return 0;
-}
-])
+AC_LANG_PROGRAM([#include <zlib.h>],
+ [deflateBound(0, 0);])])
 AC_MSG_CHECKING([for deflateBound in -lz])
 old_LIBS="$LIBS"
 LIBS="$LIBS -lz"
-AC_LINK_IFELSE(ZLIBTEST_SRC,
+AC_LINK_IFELSE([ZLIBTEST_SRC],
 	[AC_MSG_RESULT([yes])],
 	[AC_MSG_RESULT([no])
 	NO_DEFLATE_BOUND=yes])
@@ -631,23 +619,19 @@ AC_SUBST(NO_INTTYPES_H)
 #
 # Define OLD_ICONV if your library has an old iconv(), where the second
 # (input buffer pointer) parameter is declared with type (const char **).
-AC_DEFUN([OLDICONVTEST_SRC], [[
+AC_DEFUN([OLDICONVTEST_SRC], [
+AC_LANG_PROGRAM([[
 #include <iconv.h>
 
 extern size_t iconv(iconv_t cd,
 		    char **inbuf, size_t *inbytesleft,
 		    char **outbuf, size_t *outbytesleft);
-
-int main(void)
-{
-	return 0;
-}
-]])
+]], [])])
 
 GIT_STASH_FLAGS($ICONVDIR)
 
 AC_MSG_CHECKING([for old iconv()])
-AC_COMPILE_IFELSE(OLDICONVTEST_SRC,
+AC_COMPILE_IFELSE([OLDICONVTEST_SRC],
 	[AC_MSG_RESULT([no])],
 	[AC_MSG_RESULT([yes])
 	OLD_ICONV=UnfortunatelyYes])
@@ -931,18 +915,16 @@ AC_SUBST(NO_INITGROUPS)
 #
 # Define PTHREAD_LIBS to the linker flag used for Pthread support.
 AC_DEFUN([PTHREADTEST_SRC], [
+AC_LANG_PROGRAM([[
 #include <pthread.h>
-
-int main(void)
-{
+]], [[
 	pthread_mutex_t test_mutex;
 	int retcode = 0;
 	retcode |= pthread_mutex_init(&test_mutex,(void *)0);
 	retcode |= pthread_mutex_lock(&test_mutex);
 	retcode |= pthread_mutex_unlock(&test_mutex);
 	return retcode;
-}
-])
+]])])
 
 dnl AC_LANG_CONFTEST([AC_LANG_PROGRAM(
 dnl   [[#include <pthread.h>]],
@@ -962,7 +944,7 @@ elif test -z "$PTHREAD_CFLAGS"; then
      old_CFLAGS="$CFLAGS"
      CFLAGS="$opt $CFLAGS"
      AC_MSG_CHECKING([Checking for POSIX Threads with '$opt'])
-     AC_LINK_IFELSE(PTHREADTEST_SRC,
+     AC_LINK_IFELSE([PTHREADTEST_SRC],
 	[AC_MSG_RESULT([yes])
 		NO_PTHREADS=
 		PTHREAD_LIBS="$opt"
@@ -982,7 +964,7 @@ else
   old_CFLAGS="$CFLAGS"
   CFLAGS="$PTHREAD_CFLAGS $CFLAGS"
   AC_MSG_CHECKING([Checking for POSIX Threads with '$PTHREAD_CFLAGS'])
-  AC_LINK_IFELSE(PTHREADTEST_SRC,
+  AC_LINK_IFELSE([PTHREADTEST_SRC],
 	[AC_MSG_RESULT([yes])
 		NO_PTHREADS=
 		PTHREAD_LIBS="$PTHREAD_CFLAGS"