remove lto from gcc language list in sample config

afaik explicitly including lto is not necessary, and including it
breaks older gcc versions.

config.mak.dist

@@ -8,7 +8,7 @@ GCC_VER = 5.2.0
 
 # COMMON_CONFIG += --disable-nls
 # COMMON_CONFIG += MAKEINFO=/bin/false
-# GCC_CONFIG += --enable-languages=c,c++,lto
+# GCC_CONFIG += --enable-languages=c,c++
 # GCC_CONFIG += --disable-libquadmath --disable-decimal-float
 # GCC_CONFIG += --disable-multilib