Add -Wstrict-prototypes compiler warning

Disable it for the following extensions:
 - GD
 - pspell
 - readline

Closes GH-5888

Author: Girgias

Zend/Zend.m4

@@ -214,6 +214,7 @@ AX_CHECK_COMPILE_FLAG([-Wimplicit-fallthrough=1], CFLAGS="$CFLAGS -Wimplicit-fal
 AX_CHECK_COMPILE_FLAG([-Wduplicated-cond], CFLAGS="-Wduplicated-cond $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wlogical-op], CFLAGS="-Wlogical-op $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wformat-truncation], CFLAGS="-Wformat-truncation $CFLAGS", , [-Werror])
+AX_CHECK_COMPILE_FLAG([-Wstrict-prototypes], CFLAGS="-Wstrict-prototypes $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-fno-common], CFLAGS="-fno-common $CFLAGS", , [-Werror])
 
 test -n "$DEBUG_CFLAGS" && CFLAGS="$CFLAGS $DEBUG_CFLAGS"

ext/gd/config.m4

@@ -138,7 +138,8 @@ dnl
 if test "$PHP_GD" != "no"; then
 
   if test "$PHP_EXTERNAL_GD" = "no"; then
-    GD_CFLAGS=""
+    dnl Disable strict prototypes as GD takes advantages of variadic function signatures for function pointers.
+    GD_CFLAGS="-Wno-strict-prototypes"
     extra_sources="libgd/gd.c libgd/gd_gd.c libgd/gd_gd2.c libgd/gd_io.c libgd/gd_io_dp.c \
                   libgd/gd_io_file.c libgd/gd_ss.c libgd/gd_io_ss.c libgd/gd_webp.c \
                   libgd/gd_png.c libgd/gd_jpeg.c libgd/gdxpm.c libgd/gdfontt.c libgd/gdfonts.c \

ext/pspell/config.m4

@@ -4,7 +4,8 @@ PHP_ARG_WITH([pspell],
     [Include PSPELL support. GNU Aspell version 0.50.0 or higher required])])
 
 if test "$PHP_PSPELL" != "no"; then
-	PHP_NEW_EXTENSION(pspell, pspell.c, $ext_shared)
+	dnl Add -Wno-strict-prototypes as depends on user libs
+	PHP_NEW_EXTENSION(pspell, pspell.c, $ext_shared, , "-Wno-strict-prototypes")
 	if test "$PHP_PSPELL" != "yes"; then
 	    PSPELL_SEARCH_DIRS=$PHP_PSPELL
 	else

ext/readline/config.m4

@@ -137,6 +137,7 @@ elif test "$PHP_LIBEDIT" != "no"; then
 fi
 
 if test "$PHP_READLINE" != "no" || test "$PHP_LIBEDIT" != "no"; then
-  PHP_NEW_EXTENSION(readline, readline.c readline_cli.c, $ext_shared, cli)
+  dnl Add -Wno-strict-prototypes as depends on user libs
+  PHP_NEW_EXTENSION(readline, readline.c readline_cli.c, $ext_shared, cli, "-Wno-strict-prototypes")
   PHP_SUBST(READLINE_SHARED_LIBADD)
 fi