ENH: add 'Scan' WM_COMPILE_OPTION (clang only)

- backend settings for scan-build

Allwmake-scan

+#!/bin/sh
+# Allwmake with scan-build (clang)
+
+c_compiler="$(command -v $WM_CC)"
+cxx_compiler"$(command -v $WM_CXX)"
+
+set -x
+
+scan-build --use-cc="$c_compiler" --use-c++="$cxx_compiler" \
+    ./Allwmake "$@"
+
+#------------------------------------------------------------------------------

wmake/rules/linux64Clang/c++Scan

+# 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

wmake/rules/linux64Clang/cScan

+# Static analyzer with clang and Opt.
+# Call top-level Allwmake with 'scan-build' and corresponding compiler
+
+include $(DEFAULT_RULES)/cOpt
+
+c_compiler := $(shell which clang)
+cc         := $(shell echo "$(c_compiler)" | sed -e 's@/bin/[^/]*@/libexec/ccc-analyzer@') -m64