[libc][bazel] static link test targets

[michaelrj]

Summary

This solves issues caused by the symbols for internal components being
marked as hidden. When dynamically linked, the tests of internal
components, such as printf_parser_test, fail due to the symbols being
unavailable.

[gchatelet]

Thx for the patch @michaelrj !

utils/bazel/llvm-project-overlay/libc/test/libc_test_rules.bzl

def libc_test(name, srcs, libc_function_deps, deps = [], **kwargs):
     native.cc_test(
         name = name,
         srcs = srcs,
         deps = [d + INTERNAL_SUFFIX for d in all_function_deps] + [
             "//libc:libc_root",
             "//libc/test/UnitTest:LibcUnitTest",
         ] + deps,
         features = ["-link_llvmlibc"],  # Do not link libllvmlibc.a
+        linkstatic = 1,
         **kwargs
     )