Add submodules target to main makefile

See merge request redox-os/relibc!323

Adds a submodules convenience target to main makefile. Submodules must
be initialized before other targets can run successfully.

Signed-off-by: hasheddan <georgedanielmangum@gmail.com>

Fix formatiing issues

See merge request !316

Add support for dlopen(NULL, ...)

See merge request !315

Fix tls tests for dynamic linker

See merge request redox-os/relibc!317

* load TLS segment for executable - while we can skip PT_LOAD for executable,
  we still have to load TLS segment.
* set TCB address based on if elf is position independent

Add tests for ld_so

See merge request redox-os/relibc!314

Current value gives us 0x1234000 - 0x400000 ~ 14 MB for executable,
which is too low for certain programs.

Typically it's the other way around, but we can't have shared library named libc.so.6 in target/release directory.
cargo includes 'target/release' in LD_LIBRARY_PATH for build script, so even if clean build runs fine,
every subsquent run will make build script link with relibc.

Catch UB in asctime_r()

See merge request redox-os/relibc!312

Refactor gmtime_r(), fix localtime() test

See merge request redox-os/relibc!309

Add more gmtime() tests

See merge request redox-os/relibc!308

Avoid assuming c_char is i8 in asctime()

See merge request redox-os/relibc!307

Add needed include for asprintf() test

See merge request redox-os/relibc!306

link: Weaken __rust_probestack symbol

See merge request redox-os/relibc!310