autoconf: Enable threaded delta search when pthreads are supported

Automatically set THREADED_DELTA_SEARCH when autoconf test detects
support for pthreads on the platform.  This will change the default for
some platforms that did not enable threaded delta search previously.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.in

@@ -52,4 +52,5 @@ NO_DEFLATE_BOUND=@NO_DEFLATE_BOUND@
 FREAD_READS_DIRECTORIES=@FREAD_READS_DIRECTORIES@
 SNPRINTF_RETURNS_BOGUS=@SNPRINTF_RETURNS_BOGUS@
 NO_PTHREADS=@NO_PTHREADS@
+THREADED_DELTA_SEARCH=@THREADED_DELTA_SEARCH@
 PTHREAD_LIBS=@PTHREAD_LIBS@

configure.ac

@@ -492,24 +492,28 @@ AC_SUBST(NO_MKDTEMP)
 #
 # Define NO_PTHREADS if we do not have pthreads
 #
-# Define PTHREAD_LIBS to the linker flag used for Pthread support.
+# Define PTHREAD_LIBS to the linker flag used for Pthread support and define
+# THREADED_DELTA_SEARCH if Pthreads are available.
 AC_LANG_CONFTEST([AC_LANG_PROGRAM(
   [[#include <pthread.h>]],
   [[pthread_mutex_t test_mutex;]]
 )])
 ${CC} -pthread conftest.c -o conftest.o > /dev/null 2>&1
 if test $? -eq 0;then
  PTHREAD_LIBS="-pthread"
+ THREADED_DELTA_SEARCH=YesPlease
 else
  ${CC} -lpthread conftest.c -o conftest.o > /dev/null 2>&1
  if test $? -eq 0;then
   PTHREAD_LIBS="-lpthread"
+  THREADED_DELTA_SEARCH=YesPlease
  else
   NO_PTHREADS=UnfortunatelyYes
  fi
 fi
 AC_SUBST(PTHREAD_LIBS)
 AC_SUBST(NO_PTHREADS)
+AC_SUBST(THREADED_DELTA_SEARCH)
 
 ## Site configuration (override autodetection)
 ## --with-PACKAGE[=ARG] and --without-PACKAGE