[clang-repl] Disable building when LLVM_STATIC_LINK_CXX_STDLIB is ON.

We have seen random symbol not found "__cxa_throw" error in fuschia build bots and out-of-tree users. The understanding have been that they are built without exception support, but it turned out that these platforms have LLVM_STATIC_LINK_CXX_STDLIB ON so that they link libstdc++ to llvm statically. The reason why this is problematic for clang-repl is that by default clang-repl tries to find symbols from symbol table of executable and dynamic libraries loaded by current process. It needs to load another libstdc++, but the platform that had LLVM_STATIC_LINK_CXX_STDLIB turned on is usally those with missing or obsolate shared libstdc++ in the first place -- trying to load it again would be destined to fail eventually with a risk to introuduce mixed libstdc++ versions.

A proper solution that doesn't take a workaround is statically link the same libstdc++ by clang-repl side, but this is not possible with old JIT linker runtimedyld. New just...