configure: check for xlocale.h and strtof

With the assumptions that xlocale.h implies newlocale and strtof_l.  SCons is
updated to define HAVE_XLOCALE_H on linux and darwin.

Signed-off-by: Chia-I Wu <olv@lunarg.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

configure.ac

@@ -527,6 +527,9 @@ if test "x$enable_asm" = xyes; then
     esac
 fi
 
+AC_CHECK_HEADER([xlocale.h], [DEFINES="$DEFINES -DHAVE_XLOCALE_H"])
+AC_CHECK_FUNC([strtof], [DEFINES="$DEFINES -DHAVE_STRTOF"])
+
 dnl Check to see if dlopen is in default libraries (like Solaris, which
 dnl has it in libc), or if libdl is needed to get it.
 AC_CHECK_FUNC([dlopen], [DEFINES="$DEFINES -DHAVE_DLOPEN"],