New COMPILER_PLUGINS_CXX to specify compiler to build Clang plugins with

...instead of trying to second-guess what to strip off $(CXX) to make it fit.
Keep the old way for existing build scripts that rely on it.

Change-Id: I145bdcba6d02002a9b653b4deb6e7f5a9c76cc8f

compilerplugins/Makefile-clang.mk

@@ -10,10 +10,14 @@
 
 CLANG_COMMA :=,
 
-# You may occasionally want to override some of these
+ifeq ($(COMPILER_PLUGINS_CXX),)
 CLANGCXX=$(filter-out -m32 -m64 -fsanitize=%,$(CXX))
+else
+CLANGCXX=$(COMPILER_PLUGINS_CXX)
+endif
 
-# Compile flags ('make CLANGCXXFLAGS=-g' if you need to debug the plugin)
+# Compile flags ('make CLANGCXXFLAGS=-g' if you need to debug the plugin); you
+# may occasionally want to override these:
 CLANGCXXFLAGS=-O2 -Wall -Wextra -Wundef -g
 
 # The uninteresting rest.

config_host.mk.in

@@ -68,6 +68,7 @@ export COMMONS_LOGGING_JAR=@COMMONS_LOGGING_JAR@
 export COMMONS_LOGGING_VERSION=@COMMONS_LOGGING_VERSION@
 export COMPATH=@COMPATH@
 export COMPILER_PLUGINS=@COMPILER_PLUGINS@
+export COMPILER_PLUGINS_CXX=@COMPILER_PLUGINS_CXX@
 export COM_IS_CLANG=@COM_IS_CLANG@
 export CPPUNIT_CFLAGS=$(gb_SPACE)@CPPUNIT_CFLAGS@
 export CPPUNIT_LIBS=$(gb_SPACE)@CPPUNIT_LIBS@

configure.ac

@@ -6735,6 +6735,7 @@ else
     fi
 fi
 AC_SUBST(COMPILER_PLUGINS)
+AC_SUBST(COMPILER_PLUGINS_CXX)
 AC_SUBST(CLANGDIR)
 
 # Plugin to help linker.