[LLD][ThinLTO] Add --thinlto-single-module to allow compiling partial modules.

[LLD][ThinLTO] Add --thinlto-single-module to allow compiling partial modules.

This change introduces an LLD switch --thinlto-single-module to allow compiling only a part of the input modules. This is specifically enables:

  1. Fast investigating/debugging modules of interest without spending time on compiling unrelated modules.
  2. Compiler debug dump with -mllvm -debug-only= for specific modules.

It will be useful for large applications which has 1K+ input modules for thinLTO.

The switch can be combined with `--lto-obj-path=` or `--lto-emit-asm` to obtain intermediate object files or assembly files. So far the module name matching is implemented as a fuzzy name lookup where the modules with name containing the switch value are compiled.

E.g,
Command:
     ld.lld main.o thin.a --thinlto-single-module=thin.a --lto-obj-path=single.o
log:
     [ThinLTO] Selecting thin.a(thin1.o at 168) to compile
     [ThinLTO] Selecting thin.a(thin2.o at 228) to compile
Command:
     ld.lld main.o thin.a --thinlto-single-module=thin1.o --lto-obj-path=single.o
log:
     [ThinLTO] Selecting thin.a(thin1.o at 168) to compile

Differential Revision: https://reviews.llvm.org/D80406