arch: toolchain: Introduce binary formats BINFMT_*.

Just introduce the symbol and options in arch generic Config.in.
Append FLAT format link flags to external toolchain wrapper.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
diff --git a/toolchain/toolchain-external/ext-toolchain-wrapper.c b/toolchain/toolchain-external/ext-toolchain-wrapper.c
index a92bada..9a2fc70 100644
--- a/toolchain/toolchain-external/ext-toolchain-wrapper.c
+++ b/toolchain/toolchain-external/ext-toolchain-wrapper.c
@@ -47,6 +47,9 @@
 #ifdef BR_64
 	"-m64",
 #endif
+#ifdef BR_BINFMT_FLAT
+	"-Wl,-elf2flt",
+#endif
 #ifdef BR_ADDITIONAL_CFLAGS
 	BR_ADDITIONAL_CFLAGS
 #endif