builder: build static binaries using musl on Linux

This commit adds support for musl-libc and uses it by default on Linux.
The main benefit of it is that binaries are always statically linked
instead of depending on the host libc, even when using CGo.

Advantages:
  - The resulting binaries are always statically linked.
  - No need for any tools on the host OS, like a compiler, linker, or
    libc in a release build of TinyGo.
  - This also simplifies cross compilation as no cross compiler is
    needed (it's all built into the TinyGo release build).

Disadvantages:
  - Binary size increases by 5-6 kilobytes if -no-debug is used. Binary
    size increases by a much larger margin when debugging symbols are
    included (the default behavior) because musl is built with debugging
    symbols enabled.
  - Musl does things a bit differently than glibc, and some CGo code
    might rely on the glibc behavior.
  - The first build takes a bit longer because musl needs to be built.

As an additional bonus, time is now obtained from the system in a way
that fixes the Y2038 problem because musl has been a bit more agressive
in switching to 64-bit time_t.

1 files changed, 0 insertions, 0 deletions

diff --git a/lib/musl b/lib/musl
new file mode 160000
+Subproject 040c1d16b468c50c04fc94edff521f163770832