provide a cleaner way to specify a biarch toolchain build

Currently, to build a biarch toolchain, we need to explicitly give
options to the binutils and gcc configure commands:

CONFIG_EXTRA_BINUTILS_CONFIG_OPTIONS="--enable-targets=powerpc64-linux-uclibc"
CONFIG_EXTRA_GCC_CONFIG_OPTIONS="--enable-biarch --enable-targets=powerpc64-linux-uclibc"

This change replaces the command line options with an 'extra arch'
configure option:

CONFIG_EXTRA_TARGET_ARCH=y
CONFIG_EXTRA_TARGET_ARCH_NAME="powerpc64"

And a way to invoke this extra arch on the compiler command-line:

CONFIG_EXTRA_TARGET_ARCH_OPTS="-m64"

In this case, this results in an extra compiler:
 'powerpc64-linux-uclibc-gcc', which invokes
 'powerpc-linux-uclibc-gcc -m64'

This is a more standard way of building biarch toolchains, and allows
the packages to not have to care about how to invoke the 64-bit
compiler.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

SVN-Revision: 10802

toolchain/binutils/Makefile

@@ -24,6 +24,8 @@ BUILD_DIR_HOST:=$(BUILD_DIR_TOOLCHAIN)
 
 include $(INCLUDE_DIR)/host-build.mk
 
+EXTRA_TARGET=$(if $(CONFIG_EXTRA_TARGET_ARCH),--enable-targets=$(call qstrip,$(CONFIG_EXTRA_TARGET_ARCH_NAME))-linux-uclibc)
+
 define Build/Configure
 	$(CP) $(SCRIPT_DIR)/config.{guess,sub} $(PKG_BUILD_DIR)/
 	(cd $(PKG_BUILD_DIR); \
@@ -34,6 +36,7 @@ define Build/Configure
 		--target=$(REAL_GNU_TARGET_NAME) \
 		--disable-werror \
 		--disable-nls \
+		$(EXTRA_TARGET) \
 		$(SOFT_FLOAT_CONFIG_OPTION) \
 		$(call qstrip,$(CONFIG_EXTRA_BINUTILS_CONFIG_OPTIONS)) \
 	);