Add --use-clang option to configure

This also adjusts the jam files to not use $(CLANG) anymore.

build/jam/ArchitectureRules

@@ -29,7 +29,7 @@ rule ArchitectureSetup architecture
 	# http://www.freelists.org/post/haiku-development/hrev45320-Yet-another-nonobvious-effect-of-ftreevrp-optimization
 	if $(gccVersion[1]) >= 3 {
 		gccBaseFlags += -fno-strict-aliasing ;
-		if ! $(CLANG) {
+		if ! $(HAIKU_CC_IS_CLANG_$(architecture)) {
 			gccBaseFlags += -fno-tree-vrp ;
 		}
 	}
@@ -393,7 +393,7 @@ rule KernelArchitectureSetup architecture
 
 	local g++BaseFlags = $(gccBaseFlags) -fno-exceptions ;
 
-	if $(gccVersion[1]) >= 3 {
+	if $(gccVersion[1]) >= 3 && ! $(HAIKU_CC_IS_CLANG_$(architecture)) {
 		g++BaseFlags += -fno-use-cxa-atexit ;
 	}
 
@@ -498,7 +498,7 @@ rule ArchitectureSetupWarnings architecture
 	rule EnableWerror dirTokens : scope {
 		# Clang gives way more warnings than GCC, so that code won't compile
 		# -Werror when using Clang.
-		if ! $(CLANG) {
+		if ! $(HAIKU_CC_IS_CLANG_$(architecture)) {
 			SetConfigVar WARNINGS : HAIKU_TOP $(dirTokens) : treatAsErrors
 				: $(scope) ;
 		}
@@ -513,7 +513,7 @@ rule ArchitectureSetupWarnings architecture
 		WARNINGS on $(file) = $(WARNINGS) ;
 	}
 
-	if $(CLANG) {
+	if $(HAIKU_CC_IS_CLANG_$(architecture)) {
 		# We need -integrated-as, as otherwise Clang uses GCC as assembler and
 		# passes -fheinous-gnu-extensions to GCC, which GCC does not understand
 		# then errors out.

configure

@@ -86,6 +86,8 @@ options:
                               ones the secondary architectures.
   --update                    re-runs last configure invocation [must be given
                               as first option!]
+  --use-clang                 Build with host Clang instead of GCC cross
+                              compiler
   --use-gcc-pipe              Build with GCC option -pipe. Speeds up the build
                               process, but uses more memory.
   --use-gcc-graphite          Build with GCC Graphite engine for loop
@@ -352,6 +354,16 @@ standard_gcc_settings()
 	set_variable HAIKU_CPU_$targetArch $targetCpu
 
 	get_build_tool_path CC_$targetArch "$gcc"
+	if [ $useClang = 1 ]; then
+		# The get_build_tool_path above is needed to get the path to the rest
+		# of the build tools
+		local path=`dirname $(get_variable HAIKU_CC_$targetArch)`
+		set_variable HAIKU_CC_$targetArch \
+			"PATH=\\\"$path:\\\$PATH\\\" clang -target $gccMachine"
+		set_variable HAIKU_CC_IS_CLANG_$targetArch 1
+	else
+		set_variable HAIKU_CC_IS_CLANG_$targetArch 0
+	fi
 	set_variable HAIKU_GCC_RAW_VERSION_$targetArch $gccRawVersion
 	set_variable HAIKU_GCC_MACHINE_$targetArch $gccMachine
 	set_variable HAIKU_GCC_LIB_DIR_$targetArch $gccdir
@@ -454,6 +466,7 @@ targetArchs=
 buildCrossTools=
 buildCrossToolsScript="$sourceDir/build/scripts/build_cross_tools"
 buildCrossToolsJobs=
+useClang=0
 useGccGraphiteDefault=0
 unknownArchIndex=1
 haikuTargetArchs=
@@ -623,6 +636,7 @@ while [ $# -gt 0 ] ; do
 			)
 			haikuTargetArchs="$haikuTargetArchs $targetArch"
 			;;
+		--use-clang) useClang=1; shift 1;;
 		--use-gcc-pipe)	HAIKU_USE_GCC_PIPE=1; shift 1;;
 		--use-gcc-graphite)	useGccGraphiteDefault=1; shift 1;;
 		--use-32bit)	HAIKU_HOST_USE_32BIT=1; shift 1;;
@@ -907,6 +921,7 @@ for targetArch in $HAIKU_PACKAGING_ARCHS; do
 		HAIKU_BOOT_LIBSUPC++		HAIKU_BOOT_LIBSUPCXX
 		HAIKU_AR					HAIKU_AR
 		HAIKU_CC					HAIKU_CC
+		HAIKU_CC_IS_CLANG			HAIKU_CC_IS_CLANG
 		HAIKU_LD					HAIKU_LD
 		HAIKU_OBJCOPY				HAIKU_OBJCOPY
 		HAIKU_RANLIB				HAIKU_RANLIB