Check for VSVERS >= 1929

According to Microsoft, ASan is already supported as of Visual Studio
16.9, but that support might be limited, and we can't easily check
versions prior to 16.11 anyway, so we require 16.10 for now.

We also move the `ARG_ENABLE` to the top-level, since `ARG_*` has
special treatment by buildconf anyway, so there are no conditionally
declared `ARG_*`s.

Author: cmb69

win32/build/config.w32

@@ -355,15 +355,21 @@ if (PHP_SECURITY_FLAGS == "yes") {
 	ADD_FLAG("LDFLAGS", "/NXCOMPAT /DYNAMICBASE ");
 }
 
-if (CLANG_TOOLSET) {
+ARG_ENABLE("sanitizer", "Enable ASan and UBSan extensions", "no");
+if (VS_TOOLSET) {
+	if (PHP_SANITIZER == "yes") {
+		if (COMPILER_NUMERIC_VERSION < 1929) {
+			ERROR("MSVC at least 16.0 required for sanitation plugins");
+		}
+	}
+} else if (CLANG_TOOLSET) {
 	ARG_WITH("uncritical-warn-choke", "Disable some uncritical warnings", "yes");
 	if (PHP_UNCRITICAL_WARN_CHOKE != "no") {
 		ADD_FLAG("CFLAGS", "-Wno-ignored-attributes -Wno-deprecated-declarations -Wno-missing-braces " +
 		"-Wno-logical-op-parentheses -Wno-msvc-include -Wno-invalid-source-encoding -Wno-unknown-pragmas " +
 		"-Wno-unused-command-line-argument -Wno-unused-function -Wno-ignored-pragma-optimize");
 	}
 
-	ARG_ENABLE("sanitizer", "Enable ASan and UBSan extensions", "no");
 	if (PHP_SANITIZER == "yes") {
 		if (COMPILER_NUMERIC_VERSION < 500) {
 			ERROR("Clang at least 5.0.0 required for sanitation plugins");