Don't add CXXFLAGS to CFLAGS

Some CXXFLAGS such as enabling C++11 don't make sense for CC and will be
rejected, causing the compile to fail. We don't really test for flags being
compatible with the C compiler anyway, and we don't have enough C files to
care that much.

infrastructure/makebuildenv.pl.in

@@ -410,7 +410,7 @@ WINDRES = @WINDRES@
 
 # Work around a mistake in QDBM (using <angled> includes for a file not in the
 # system path) by adding it to the include path with -I.
-DEFAULT_CFLAGS = $autoconf_cppflags $default_cflags $autoconf_cxxflags \\
+DEFAULT_CFLAGS = $autoconf_cppflags $default_cflags \\
 	$extra_platform_defines $platform_compile_line_extra \\
 	-DBOX_VERSION="\\"$product_version\\"" -Iqdbm
 DEFAULT_CXXFLAGS = $autoconf_cppflags $default_cxxflags $autoconf_cxxflags \\