litecross: add some gcc options that should always be used with musl

libmpx is broken in all gcc versions that have it (not supported yet
by mcm/litecross, but will be).

ifunc is not supported by musl and won't be unless/until the contract
for resolvers can be specified clearly in a way that real-world usage
is safe and does not require lazy binding; having it enabled at gcc
level reportedly produces a broken libatomic.

explicitly enabling libstdcxx-time is needed to get libc clock_gettime
(with vdso support) to be used in libstdc++; it's disabled by default
because of glibc legacy practice of having clock_gettime in librt,
which depends on glibc's libpthread and undermines libstdc++'s
(invalid use of) weak references to pthread symbols.

litecross/Makefile

@@ -25,7 +25,10 @@ FULL_TOOLCHAIN_CONFIG = $(TOOLCHAIN_CONFIG) \
 	--with-sysroot=$(SYSROOT) \
 	--with-build-sysroot='$$(LC_ROOT)/obj_sysroot' \
 	--enable-tls \
-	--disable-libmudflap --disable-libsanitizer
+	--disable-libmudflap --disable-libsanitizer \
+	--disable-gnu-indirect-function \
+	--disable-libmpx \
+	--enable-libstdcxx-time
 
 FULL_MUSL_CONFIG = $(MUSL_CONFIG) \
 	--prefix= --host=$(TARGET)