Use level 1 for -Wimplicit-fallthrough instead of default level 3 from Wextra

Author: Girgias

Zend/Zend.m4

@@ -206,7 +206,7 @@ else
   AC_DEFINE(ZEND_DEBUG,0,[ ])
 fi
 
-test -n "$GCC" && CFLAGS="-Wall -Wextra -Wno-strict-aliasing -Wno-unused-parameter -Wno-sign-compare $CFLAGS"
+test -n "$GCC" && CFLAGS="-Wall -Wextra -Wimplicit-fallthrough=1 -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])