Drop -Wno-implicit-fallthrough compiler flag

And add it back to ext/date, ext/hash, and ext/opcache

Author: Girgias

UPGRADING.INTERNALS

@@ -6,6 +6,7 @@ PHP 8.1 INTERNALS UPGRADE NOTES
   c. zend_get_opcode_id()
 
 2. Build system changes
+  a. New compiler flags
 
 3. Module changes
   a. ext/hash
@@ -39,7 +40,8 @@ PHP 8.1 INTERNALS UPGRADE NOTES
 ========================
 2. Build system changes
 ========================
-
+  a. New compiler flags
+     - [-Wimplicit-fallthrough=1] is now enabled by default
 ========================
 3. Module changes
 ========================

Zend/Zend.m4

@@ -206,7 +206,7 @@ else
   AC_DEFINE(ZEND_DEBUG,0,[ ])
 fi
 
-test -n "$GCC" && CFLAGS="-Wall -Wextra -Wno-strict-aliasing -Wno-implicit-fallthrough -Wno-unused-parameter -Wno-sign-compare $CFLAGS"
+test -n "$GCC" && CFLAGS="-Wall -Wextra -Wno-strict-aliasing -Wno-unused-parameter -Wno-sign-compare $CFLAGS"
 dnl Check if compiler supports -Wno-clobbered (only GCC)
 AX_CHECK_COMPILE_FLAG([-Wno-clobbered], CFLAGS="-Wno-clobbered $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wduplicated-cond], CFLAGS="-Wduplicated-cond $CFLAGS", , [-Werror])

ext/date/config0.m4

@@ -4,7 +4,7 @@ AC_CHECK_HEADERS([io.h])
 dnl Check for strtoll, atoll
 AC_CHECK_FUNCS(strtoll atoll)
 
-PHP_DATE_CFLAGS="-I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
+PHP_DATE_CFLAGS="-Wno-implicit-fallthrough -I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
 timelib_sources="lib/astro.c lib/dow.c lib/parse_date.c lib/parse_tz.c lib/parse_posix.c
                  lib/timelib.c lib/tm2unixtime.c lib/unixtime2tm.c lib/parse_iso_intervals.c lib/interval.c"
 

ext/hash/config.m4

@@ -28,7 +28,8 @@ else
     SHA3_OPT_SRC="$SHA3_DIR/KeccakP-1600-opt64.c"
   ])
   EXT_HASH_SHA3_SOURCES="$SHA3_OPT_SRC $SHA3_DIR/KeccakHash.c $SHA3_DIR/KeccakSponge.c hash_sha3.c"
-  PHP_HASH_CFLAGS="-I@ext_srcdir@/$SHA3_DIR -DKeccakP200_excluded -DKeccakP400_excluded -DKeccakP800_excluded -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
+  dnl Add -Wno-implicit-fallthrough flag as it happens on 32 bit builds
+  PHP_HASH_CFLAGS="-Wno-implicit-fallthrough -I@ext_srcdir@/$SHA3_DIR -DKeccakP200_excluded -DKeccakP400_excluded -DKeccakP800_excluded -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
 
   PHP_ADD_BUILD_DIR(ext/hash/$SHA3_DIR, 1)
 fi

ext/opcache/config.m4

@@ -321,7 +321,7 @@ int main() {
 	shared_alloc_mmap.c \
 	shared_alloc_posix.c \
 	$ZEND_JIT_SRC,
-	shared,,-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1,,yes)
+	shared,,"-Wno-implicit-fallthrough -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1",,yes)
 
   PHP_ADD_EXTENSION_DEP(opcache, pcre)