Run __libc_start_main directly

Change relinterp.c from a chain loader that jumps to _start to
a replacement crt that implements _start and jumps to
__libc_start_main when it is done.  This makes it only work for
musl, but reduces the complexity of compiling against it by
removing the need to override the entry point to __ri__start.

Bug: 242601708
Test: m USE_HOST_MUSL=true bzip2
Change-Id: Ib9b5530d3a8c533b2e6ccde72fb301aab742a835
3 files changed