Expand external toolchain wrapper to custom flags

The BR2_TARGET_OPTIMIZATION flags were not used by the external
toolchain wrapper, which broke the multilib selection logic of
multilib external toolchains. It also simplifies the compilation of
external programs since all flags are properly passed automatically by
the toolchain wrapper.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/toolchain-external/ext-tool.mk

@@ -150,6 +150,14 @@ TOOLCHAIN_EXTERNAL_CFLAGS += -mabi=$(CC_TARGET_ABI_)
 TOOLCHAIN_EXTERNAL_WRAPPER_ARGS += -DBR_ABI='"$(CC_TARGET_ABI_)"'
 endif
 
+ifneq ($(BR2_TARGET_OPTIMIZATION),)
+TOOLCHAIN_EXTERNAL_CFLAGS += $(call qstrip,$(BR2_TARGET_OPTIMIZATION))
+# We create a list like '"-mfoo", "-mbar", "-mbarfoo"' so that each
+# flag is a separate argument when used in execv() by the external
+# toolchain wrapper.
+TOOLCHAIN_EXTERNAL_WRAPPER_ARGS += -DBR_ADDITIONAL_CFLAGS='$(foreach f,$(call qstrip,$(BR2_TARGET_OPTIMIZATION)),"$(f)",)'
+endif
+
 ifeq ($(BR2_SOFT_FLOAT),y)
 TOOLCHAIN_EXTERNAL_CFLAGS += -msoft-float
 TOOLCHAIN_EXTERNAL_WRAPPER_ARGS += -DBR_SOFTFLOAT=1

toolchain/toolchain-external/ext-toolchain-wrapper.c

@@ -40,6 +40,9 @@ static char *predef_args[] = {
 #ifdef BR_VFPFLOAT
 	"-mfpu=vfp",
 #endif /* BR_VFPFLOAT */
+#ifdef BR_ADDITIONAL_CFLAGS
+	BR_ADDITIONAL_CFLAGS
+#endif
 };
 
 static const char *get_basename(const char *name)