* it is now -fcompiler-rt and -fno-compiler-rt to override the (quite
   reasonable) default of bundling compiler-rt only for executables and
   dynamic libraries.
   - the build.zig API is still called bundle_compiler_rt however it is
     now an optional bool instead of a bool. leaving it as `null` means
     to use the compiler default.
 * renamed some internal identifiers to make the source more readable
 * additionally support -fcompiler-rt when doing build-obj for ELF files
   since that target already supports linking multiple objects into one.
   - includes an error message when attempting this for non-ELF. in the
     future this could additionally be supported with a more advanced
     implementation that does not rely on the linker.
 * properly populate the linker cache hash