gcc: allow optional colorized diagnostics output

which is nice, so people who like this are able to see their gcc diagnostics
in full color. It's even possible to change the colors for non ubuntu like
dark background terminals.

gcc.be0

@@ -1,6 +1,6 @@
 #!/bin/env beesh
 
-# BEE_VERSION gcc-7.3.0-1
+# BEE_VERSION gcc-7.3.0-2
 
 # Note: The test suite runs address sanitizer tests. In the current mariux64 environment
 # this requires
@@ -29,7 +29,8 @@ mee_configure() {
        --enable-clocale=gnu \
        --enable-languages=c,fortran,c++,objc,obj-c++ \
        --disable-multilib \
-       --with-system-zlib
+       --with-system-zlib \
+       --with-diagnostics-color=auto-if-env
 }
 
 mee_check() {