[BOLT] Support for lite mode with relocations

Summary:
Add '-lite' support for relocations for improved processing time,
memory consumption, and more resilient processing of binaries with
embedded assembly code.

In lite relocation mode, BOLT will skip full processing of functions
without a profile. It will run scanExternalRefs() on such functions
to discover external references and to create internal relocations
to update references to optimized functions.

Note that we could have relied on the compiler/linker to provide
relocations for function references. However, there's no assurance
that all such references are reported. E.g., the compiler can resolve
inter-procedural references internally, leaving no relocations
for the linker.

The scan process takes about <10 seconds per 100MB of code on modern
hardware. It's a reasonable overhead to live with considering the
flexibility it provides.

If BOLT fails to scan or disassemble a function, .e.g., due to a data
object embedded in code, or an unsupported instruction, it enables a
patching mode to guarantee that the failed function will call
optimized/moved versions of functions. The patching happens at original
function entry points.

'-skip=<func1,func2,...>' option now can be used to skip processing of
arbitrary functions in the relocation mode.

With '-use-old-text' or '-strict' we require all functions to be
processed. As such, it is incompatible with '-lite' option,
and '-skip' option will only disable optimizations of listed
functions, not their disassembly and emission.

(cherry picked from FBD22040717)