Auto-detect target arch via cross-compiler. Drop TARGET=arch.

src/Makefile

@@ -173,13 +173,11 @@ XCFLAGS=
 #
 # Cross-compilation examples:
 #   make HOST_CC="gcc -m32" CROSS=i586-mingw32msvc- TARGET_SYS=Windows
-#   make HOST_CC="gcc -m32" CROSS=powerpc-e500v2-linux-gnuspe- TARGET=ppcspe
+#   make HOST_CC="gcc -m32" CROSS=powerpc-linux-gnu-
 
 CCOPTIONS= $(CCDEBUG) $(CCOPT) $(CCWARN) $(XCFLAGS) $(CFLAGS)
 LDOPTIONS= $(CCDEBUG) $(LDFLAGS)
 
-TARGET_ARCH= $(patsubst %,-DLUAJIT_TARGET=LUAJIT_ARCH_%,$(TARGET))
-
 HOST_CC= $(CC)
 HOST_RM= rm -f
 # NOTE: The LuaJIT distribution comes with pre-generated buildvm_*.h files.
@@ -214,6 +212,7 @@ TARGET_DYNXLDOPTS=
 TARGET_XCFLAGS= -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -U_FORTIFY_SOURCE
 TARGET_XLDFLAGS=
 TARGET_XLIBS= -lm
+TARGET_TCFLAGS= $(CCOPTIONS) $(TARGET_XCFLAGS) $(TARGET_FLAGS) $(TARGET_CFLAGS)
 TARGET_ACFLAGS= $(CCOPTIONS) $(TARGET_XCFLAGS) $(TARGET_ARCH) $(TARGET_FLAGS) $(TARGET_CFLAGS)
 TARGET_ALDFLAGS= $(LDOPTIONS) $(TARGET_XLDFLAGS) $(TARGET_FLAGS) $(TARGET_LDFLAGS)
 TARGET_ASHLDFLAGS= $(LDOPTIONS) $(TARGET_XSHLDFLAGS) $(TARGET_FLAGS) $(TARGET_SHLDFLAGS)
@@ -223,7 +222,7 @@ ifneq (,$(findstring stack-protector,$(shell $(TARGET_CC) -dumpspecs)))
   TARGET_XCFLAGS+= -fno-stack-protector
 endif
 
-TARGET_TESTARCH=$(shell $(TARGET_CC) $(TARGET_ACFLAGS) -E lj_arch.h -dM)
+TARGET_TESTARCH=$(shell $(TARGET_CC) $(TARGET_TCFLAGS) -E lj_arch.h -dM)
 ifneq (,$(findstring LJ_TARGET_X64 ,$(TARGET_TESTARCH)))
   TARGET_CCARCH= x64
   TARGET_XCFLAGS+= $(CCOPT_X64)
@@ -251,6 +250,8 @@ endif
 endif
 endif
 
+TARGET_ARCH= $(patsubst %,-DLUAJIT_TARGET=LUAJIT_ARCH_%,$(TARGET_CCARCH))
+
 ifneq (,$(PREFIX))
 ifneq (/usr/local,$(PREFIX))
   TARGET_XCFLAGS+= -DLUA_XROOT=\"$(PREFIX)/\"