[6.0] 2766d16aa build: Better handle zlib-specific C flags

[Dridi Boukelmoune]

commit 2766d16aacde26e9cb4e262939d0a27c33a1e0e2
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Mon Jan 30 11:27:57 2023 +0100

    build: Better handle zlib-specific C flags
    
    There are two warnings that we enforce for our own code that zlib does
    not. There's also the visibility attribute that we check at configure
    time. And regarding the visibility attribute, zlib no longer relies on
    a NO_VIZ macro and aligned with the autoconf naming convention and wants
    HAVE_HIDDEN instead.
    
    Conflicts:
            configure.ac
            lib/libvgz/Makefile.am

diff --git a/configure.ac b/configure.ac
index ca100e06c..3baa78565 100644
--- a/configure.ac
+++ b/configure.ac
@@ -244,29 +244,25 @@ AC_CHECK_FUNCS([pthread_setname_np])
 AC_CHECK_FUNCS([pthread_mutex_isowned_np])
 LIBS="${save_LIBS}"
 
-# Support for visibility attribute
-save_CFLAGS="${CFLAGS}"
-CFLAGS="${CFLAGS} -Werror"
+# zlib-specific flags
+libvgz_extra_cflags="-Wno-error=strict-prototypes"
 
+dnl https://github.com/madler/zlib/issues/633
+libvgz_extra_cflags="$libvgz_extra_cflags -Wno-error=deprecated-non-prototype"
+
+AC_SUBST(libvgz_extra_cflags)
+
+# Support for visibility attribute (zlib)
 AC_CACHE_CHECK([whether we have support for visibility attributes],
 	[ac_cv_have_viz],
-	[AC_RUN_IFELSE(
+	[AC_COMPILE_IFELSE(
 		[AC_LANG_PROGRAM([[
-			#if ((__GNUC__-0) * 10 + __GNUC_MINOR__-0 >= 33)
-			#  define ZLIB_INTERNAL __attribute__((visibility ("hidden")))
-			#else
-			#  define ZLIB_INTERNAL
-			#endif
-			int ZLIB_INTERNAL foo;
+			int __attribute__((visibility ("hidden"))) foo;
 		]],[])],
-	[ac_cv_have_viz=yes],
-	[ac_cv_have_viz=no])
+	[AC_DEFINE([HAVE_HIDDEN], [1],
+		[Define to 1 if visibility attribute hidden is available.])
+	])
 ])
-if test "$ac_cv_have_viz" = no; then
-	libvgz_extra_cflags="-DNO_VIZ"
-	AC_SUBST(libvgz_extra_cflags)
-fi
-CFLAGS="${save_CFLAGS}"
 
 if test "x$GCC" = "xyes"; then
 	libvgz_extra_cflags="${libvgz_extra_cflags} -Wno-unknown-warning-option -Wno-implicit-fallthrough"
diff --git a/lib/libvgz/Makefile.am b/lib/libvgz/Makefile.am
index db9a48bdc..e6f7a1dbe 100644
--- a/lib/libvgz/Makefile.am
+++ b/lib/libvgz/Makefile.am
@@ -1,11 +1,14 @@
 #
 
-AM_LDFLAGS  = $(AM_LT_LDFLAGS)
+AM_CFLAGS = $(AM_LT_CFLAGS) \
+	-D_LARGEFILE64_SOURCE=1 \
+	-DZLIB_CONST \
+	$(libvgz_extra_cflags) \
+	@SAN_CFLAGS@
 
-noinst_LIBRARIES = libvgz.a
+AM_LDFLAGS = $(AM_LT_LDFLAGS)
 
-libvgz_a_CFLAGS = -D_LARGEFILE64_SOURCE=1 -DZLIB_CONST \
-	$(libvgz_extra_cflags) @SAN_CFLAGS@
+noinst_LIBRARIES = libvgz.a
 
 libvgz_a_SOURCES = \
 	adler32.c \