[master] 79c7d1754 build: Revisit zlib C flags one more time

[Dridi Boukelmoune]

commit 79c7d17543d86249c9e88ca1cf2a14f423275fff
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Mon Jan 30 13:54:13 2023 +0100

    build: Revisit zlib C flags one more time
    
    Trying to fix the build for clang 15 actually broke the build for GCC.
    
    The -Werror that was initially set after saving CFLAGS was meant to be
    part of NO_VIZ test. We turn warnings into errors later in the configure
    script so at this point we shouldn't care about it. If we really do, we
    can move this check below the line where -Werror is set.
    
    GCC chokes on -Wno-error=deprecated-non-prototype so instead we add it
    conditionally.
    
    To match the naming convention everywhere else, libvgz_extra_cflags was
    renamed to VGZ_CFLAGS.
    
    Refs 118fd10c9e81920e0c31906c2bf5c62a3f25cd5b

diff --git a/configure.ac b/configure.ac
index c21d6bf63..9596b8285 100644
--- a/configure.ac
+++ b/configure.ac
@@ -249,19 +249,14 @@ LIBS="${save_LIBS}"
 
 AC_CHECK_DECL([__SUNPRO_C], [SUNCC="yes"], [SUNCC="no"])
 
-if test "$SUNCC" = "yes" ; then
-	CFLAGS="${CFLAGS} -errwarn=%all,no%E_EMPTY_TRANSLATION_UNIT"
-else
-	CFLAGS="${CFLAGS} -Werror"
-fi
-
 # zlib-specific flags
-libvgz_extra_cflags="-Wno-error=strict-prototypes -Wno-unknown-warning-option"
+VGZ_CFLAGS="-Wno-error=strict-prototypes -Wno-unknown-warning-option"
 
 dnl https://github.com/madler/zlib/issues/633
-libvgz_extra_cflags="$libvgz_extra_cflags -Wno-error=deprecated-non-prototype"
+AX_CHECK_COMPILE_FLAG([-Wno-error=deprecated-non-prototype],
+	[VGZ_CFLAGS="$VGZ_CFLAGS -Wno-error=deprecated-non-prototype"])
 
-AC_SUBST(libvgz_extra_cflags)
+AC_SUBST(VGZ_CFLAGS)
 
 # Support for visibility attribute (zlib)
 AC_CACHE_CHECK([whether we have support for visibility attributes],
diff --git a/lib/libvgz/Makefile.am b/lib/libvgz/Makefile.am
index 929646ad5..bbca6f5ac 100644
--- a/lib/libvgz/Makefile.am
+++ b/lib/libvgz/Makefile.am
@@ -3,7 +3,7 @@
 AM_CFLAGS = $(AM_LT_CFLAGS) \
 	-D_LARGEFILE64_SOURCE=1 \
 	-DZLIB_CONST \
-	$(libvgz_extra_cflags)
+	$(VGZ_CFLAGS)
 
 AM_LDFLAGS = $(AM_LT_LDFLAGS)