toolchain/gcc: Only enable --with-float when it makes sense

According to gcc/config.gcc, only ARM, MIPS and SPARC have the
"--with-float" option when configuring gcc.

[Peter: sort list]
Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/gcc/gcc-uclibc-4.x.mk

@@ -65,7 +65,10 @@ endif
 
 # Determine soft-float options
 ifeq ($(BR2_SOFT_FLOAT),y)
+# only mips*-*-*, arm*-*-* and sparc*-*-* accept --with-float
+ifeq ($(BR2_arm)$(BR2_armeb)$(BR2_mips)$(BR2_mipsel)$(BR2_mips64)$(BR2_mips64el)$(BR2_sparc),y)
 SOFT_FLOAT_CONFIG_OPTION:=--with-float=soft
+endif
 ifeq ($(BR2_arm)$(BR2_armeb),y) # only set float-abi for arm
 TARGET_SOFT_FLOAT:=-mfloat-abi=soft
 else