Add support for selectively enabling LLVM targets

This makes it possible, through src.conf(5) settings, to select which
LLVM targets you want to build during buildworld.  The current list is:

* (WITH|WITHOUT)_LLVM_TARGET_AARCH64
* (WITH|WITHOUT)_LLVM_TARGET_ARM
* (WITH|WITHOUT)_LLVM_TARGET_MIPS
* (WITH|WITHOUT)_LLVM_TARGET_POWERPC
* (WITH|WITHOUT)_LLVM_TARGET_SPARC
* (WITH|WITHOUT)_LLVM_TARGET_X86

To not influence anything right now, all of these are on by default, in
situations where clang is enabled.

Selectively turning a few targets off manually should work.  Turning on
only one target should work too, even if that target does not correspond
to the build architecture.  (In that case, LLVM_NATIVE_ARCH will not be
defined, and you can only use the resulting clang executable for
cross-compiling.)

I performed a few measurements on one of the FreeBSD.org reference
machines, building clang from scratch, with all targets enabled, and
with only the x86 target enabled.  The latter was ~12% faster in real
time (on a 32-core box), and ~14% faster in user time.  For a full
buildworld the difference will probably be less pronounced, though.

Reviewed by:	bdrewery
MFC after:	1 week
Differential Revision: https://reviews.freebsd.org/D11077

1 files changed, 48 insertions, 0 deletions

diff --git a/lib/clang/llvm.build.mk b/lib/clang/llvm.build.mk
index 861b97a37172..b8b4d9b0500e 100644
--- a/lib/clang/llvm.build.mk
+++ b/lib/clang/llvm.build.mk
@@ -1,5 +1,7 @@
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 .ifndef LLVM_SRCS
 .error Please define LLVM_SRCS before including this file
 .endif
@@ -40,6 +42,52 @@ CFLAGS+=	-DLLVM_DEFAULT_TARGET_TRIPLE=\"${LLVM_TARGET_TRIPLE}\"
 CFLAGS+=	-DLLVM_HOST_TRIPLE=\"${LLVM_BUILD_TRIPLE}\"
 CFLAGS+=	-DDEFAULT_SYSROOT=\"${TOOLS_PREFIX}\"
 
+.if ${MK_LLVM_TARGET_AARCH64} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_AARCH64
+. if ${MACHINE_CPUARCH} == "aarch64"
+LLVM_NATIVE_ARCH=	AArch64
+. endif
+.endif
+.if ${MK_LLVM_TARGET_ARM} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_ARM
+. if ${MACHINE_CPUARCH} == "arm"
+LLVM_NATIVE_ARCH=	ARM
+. endif
+.endif
+.if ${MK_LLVM_TARGET_MIPS} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_MIPS
+. if ${MACHINE_CPUARCH} == "mips"
+LLVM_NATIVE_ARCH=	Mips
+. endif
+.endif
+.if ${MK_LLVM_TARGET_POWERPC} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_POWERPC
+. if ${MACHINE_CPUARCH} == "powerpc"
+LLVM_NATIVE_ARCH=	PowerPC
+. endif
+.endif
+.if ${MK_LLVM_TARGET_SPARC} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_SPARC
+. if ${MACHINE_CPUARCH} == "sparc64"
+LLVM_NATIVE_ARCH=	Sparc
+. endif
+.endif
+.if ${MK_LLVM_TARGET_X86} != "no"
+CFLAGS+=	-DLLVM_TARGET_ENABLE_X86
+. if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
+LLVM_NATIVE_ARCH=	X86
+. endif
+.endif
+
+.ifdef LLVM_NATIVE_ARCH
+CFLAGS+=	-DLLVM_NATIVE_ASMPARSER=LLVMInitialize${LLVM_NATIVE_ARCH}AsmParser
+CFLAGS+=	-DLLVM_NATIVE_ASMPRINTER=LLVMInitialize${LLVM_NATIVE_ARCH}AsmPrinter
+CFLAGS+=	-DLLVM_NATIVE_DISASSEMBLER=LLVMInitialize${LLVM_NATIVE_ARCH}Disassembler
+CFLAGS+=	-DLLVM_NATIVE_TARGET=LLVMInitialize${LLVM_NATIVE_ARCH}Target
+CFLAGS+=	-DLLVM_NATIVE_TARGETINFO=LLVMInitialize${LLVM_NATIVE_ARCH}TargetInfo
+CFLAGS+=	-DLLVM_NATIVE_TARGETMC=LLVMInitialize${LLVM_NATIVE_ARCH}TargetMC
+.endif
+
 CFLAGS+=	-ffunction-sections
 CFLAGS+=	-fdata-sections
 LDFLAGS+=	-Wl,--gc-sections