Update gcc_build.

 - Enable shared build of gcc.
 - Fix dl_files/decomp_arch functions.
Update buildscripts.

 - ffmpeg.sh: clock_gettime/nanosleep are enabled when using gcc which
              is enabled shared build, and thread model of which is posix.
              However, MSVC doesn't have these functions.
 - lsw.sh: link statically to gcc shared dll.
gcc_build/gcc: Enable colorizing diagnostics.

Enabled by default.
Force cmd to use utf-8.
Update gcc_build.

gcc: Add more patches.
 - 0013/0014: Don't search dirs under ${prefix} but ${build_sysroot}.
              symlink [/mingw] is not needed any more.
 - 0015: From tdm.
gcc: Add ${_CPPFLAGS} to CFLAGS/CXXFLAGS.
    GCC doesn't pass CPPFLAGS...
winpthread: Add preprocessor flag (-DWINPTHREAD_STATIC).
    The patch is from tdm.
buildscripts: Use /mingw{32,64}/local for prefix.