libtool: Add CC tag explicitly

This fixes the scan-build build. CC is also the default tag, so there
should be no impact anywhere.

Signed-off-by: Anatol Belski <ab@php.net>

configure.ac

@@ -1535,6 +1535,9 @@ PHP_SET_LIBTOOL_VARIABLE([--silent])
 dnl libtool 1.4.3 needs this.
 PHP_SET_LIBTOOL_VARIABLE([--preserve-dup-deps])
 
+dnl This needs to be passed explicitly to allow scan-build compiler overrides.
+PHP_SET_LIBTOOL_VARIABLE([--tag CC])
+
 test -z "$PHP_COMPILE" && PHP_COMPILE='$(LIBTOOL) --mode=compile $(COMPILE) -c $<'
 test -z "$CXX_PHP_COMPILE" && CXX_PHP_COMPILE='$(LIBTOOL) --mode=compile $(CXX_COMPILE) -c $<'
 SHARED_LIBTOOL='$(LIBTOOL)'