ENH: add 'Scan' WM_COMPILE_OPTION (clang only)

- backend settings for scan-build

wmake/rules/linux64Clang/c++Scan

@@ -0,0 +1,7 @@
+# Static analyzer with clang and Opt.
+# Call top-level Allwmake with 'scan-build' and corresponding compiler
+
+include $(DEFAULT_RULES)/c++Opt
+
+cxx_compiler := $(shell which clang++)
+CC         := $(shell echo "$(cxx_compiler)" | sed -e 's@/bin/[^/]*@/libexec/c++-analyzer@') -std=c++11 -m64