arch/Config.in.mips: add support for XBurst cores

The Ingenic XBurst is a MIPS32R2 microprocessor.

It has a bug in the FPU that can generate incorrect results in certain
cases. The problem shows up when you have several fused madd
instructions in sequence with dependant operands.

Using the -mno-fused-madd option prevents gcc from emitting these
instructions. This patch adds changes to the toolchain wrapper to use
that option.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/toolchain-wrapper.c

@@ -66,6 +66,9 @@ static char *predef_args[] = {
 #ifdef BR_OMIT_LOCK_PREFIX
 	"-Wa,-momit-lock-prefix=yes",
 #endif
+#ifdef BR_NO_FUSED_MADD
+	"-mno-fused-madd",
+#endif
 #ifdef BR_BINFMT_FLAT
 	"-Wl,-elf2flt",
 #endif

toolchain/toolchain-wrapper.mk

@@ -26,6 +26,11 @@ ifeq ($(BR2_x86_x1000),y)
 TOOLCHAIN_WRAPPER_ARGS += -DBR_OMIT_LOCK_PREFIX
 endif
 
+# Avoid FPU bug on XBurst CPUs
+ifeq ($(BR2_mips_xburst),y)
+TOOLCHAIN_WRAPPER_ARGS += -DBR_NO_FUSED_MADD
+endif
+
 ifeq ($(BR2_CCACHE_USE_BASEDIR),y)
 TOOLCHAIN_WRAPPER_ARGS += -DBR_CCACHE_BASEDIR='"$(BASE_DIR)"'
 endif