Steps towards MSVC compatibility

Add USEMSVC variable to Make.inc for handling different flags and toolchain

Fix LLVM header problem in codegen.cpp due to define on min/max

Use __cpuid intrinsic for msvc instead of inline assembly

Add explicit casts, fixup ifdefs (_WIN32 instead of __WIN32__)
Updates for MSVC

patch utf8proc so it can compile in either C or C++ mode

dont define USE_COMPUTED_GOTO for MSVC
(might be an odd double-definition problem from some header)

add utf8proc info to src/flisp/Windows.mk
(needs some improvement on handling of utf8proc
version number and assumption of cl vs icl)

add strtod to Windows.mk

add DLLEXPORT before jl_init_frontend(void)

modify OSLIBS and CONFIGURE_COMMON for msvc
compile basename and dirname for msvc
adjust linker invocation for msvc
skip flisp unit test with msvc (for now?)
disable line endings error
define HUGE_VALF if needed