Sync -Wno-implicit-fallthrough

This is a sync of the https://github.com/php/php-src/pull/6252 after few
years:
- ext/date: pending recheck in GH-14187
- ext/hash: warning happens only on 32-bit build in
  ext/hash/sha3/generic32lc/KeccakP-1600-inplace32BI.c
- ext/opcache: IR JIT doesn't seem to have this issue
- ext/pcre remains disabled due to pcre2lib/sljit/sljitNativeARM_64.c
  (should be rechecked and fixed upstream)

ext/hash/config.m4

@@ -19,14 +19,15 @@ else
     AC_MSG_RESULT([no])
     SHA3_DIR="sha3/generic32lc"
     SHA3_OPT_SRC="$SHA3_DIR/KeccakP-1600-inplace32BI.c"
+    dnl Add -Wno-implicit-fallthrough flag as it happens on 32 bit builds
+    PHP_HASH_CFLAGS="-Wno-implicit-fallthrough"
   ],[
     AC_MSG_RESULT([yes])
     SHA3_DIR="sha3/generic64lc"
     SHA3_OPT_SRC="$SHA3_DIR/KeccakP-1600-opt64.c"
   ])
   EXT_HASH_SHA3_SOURCES="$SHA3_OPT_SRC $SHA3_DIR/KeccakHash.c $SHA3_DIR/KeccakSponge.c hash_sha3.c"
-  dnl Add -Wno-implicit-fallthrough flag as it happens on 32 bit builds
-  PHP_HASH_CFLAGS="-Wno-implicit-fallthrough -I@ext_srcdir@/$SHA3_DIR -DKeccakP200_excluded -DKeccakP400_excluded -DKeccakP800_excluded -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
+  PHP_HASH_CFLAGS="$PHP_HASH_CFLAGS -I@ext_srcdir@/$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

@@ -337,7 +337,7 @@ int main(void) {
 	shared_alloc_mmap.c \
 	shared_alloc_posix.c \
 	$ZEND_JIT_SRC,
-	shared,,"-Wno-implicit-fallthrough -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 ${JIT_CFLAGS}",,yes)
+	shared,,"-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 ${JIT_CFLAGS}",,yes)
 
   PHP_ADD_EXTENSION_DEP(opcache, pcre)