Define PHP_HAVE_BUILTIN_EXPECT for Clang on Windows

Clang supports `__builtin_expect()` at least as of 4.0.0, which is the
(theoretical) minimum required on Windows, so we define it
unconditionally.  This also solves some macro redefinition warnings in
JIT-IR.

win32/build/config.w32

@@ -370,6 +370,7 @@ if (VS_TOOLSET) {
 		}
 	}
 } else if (CLANG_TOOLSET) {
+	AC_DEFINE("PHP_HAVE_BUILTIN_EXPECT", 1, "Define to 1 if the compiler supports '__builtin_expect'.");
 	AC_DEFINE("PHP_HAVE_BUILTIN_SADDL_OVERFLOW", 1, "Define to 1 if the compiler supports '__builtin_saddl_overflow'.");
 	AC_DEFINE("PHP_HAVE_BUILTIN_SADDLL_OVERFLOW", 1, "Define to 1 if the compiler supports '__builtin_saddll_overflow'.");
 	AC_DEFINE("PHP_HAVE_BUILTIN_SSUBL_OVERFLOW", 1, "Define to 1 if the compiler supports '__builtin_ssubl_overflow'.");