fix build for s390x due to wrong long double ABI default

musl uses IEEE quad for long double on s390x. current versions check
for mismatch and hard fail at configure time if the compiler is wrong.
with older versions, mcm silently produced a broken toolchain/libc.

litecross/Makefile

@@ -35,6 +35,10 @@ GCC_CONFIG_FOR_TARGET += --with-abi=64
 endif
 endif
 
+ifneq ($(findstring s390x,$(TARGET)),)
+GCC_CONFIG_FOR_TARGET += --with-long-double-128
+endif
+
 ifneq ($(filter %sf,$(TARGET)),)
 GCC_CONFIG_FOR_TARGET += --with-float=soft
 endif