[clang][docs] Document ThinLTO options for ld64.lld

[int3]

Summary

The LTO-cache-related flags were added here: D105922: [lld-macho] Add LTO cache support

[tejohnson]

lgtm with one additional stale comment fix needed.

clang/docs/ThinLTO.rst

155–156

Needs an update to add Mach-O to the lld list. Or maybe "only gold and lld" suffices now since it sounds like all lld formats support this now.

clang/docs/ThinLTO.rst

 virtual cores. For some applications and machine configurations this
 may be too aggressive, in which case the amount of parallelism can
 be reduced to ``N`` via:
 
 - gold:
   ``-Wl,-plugin-opt,jobs=N``
 - ld64:
   ``-Wl,-mllvm,-threads=N``
-- lld:
+- ld.lld, ld64.lld:
   ``-Wl,--thinlto-jobs=N``
 - lld-link:
   ``/opt:lldltojobs=N``
 
 Other possible values for ``N`` are:
 
 - 0:
   Use one thread per physical core (default)
 - 1:
   Use a single thread only (disable multi-threading)
 - all:
   Use one thread per logical core (uses all hyper-threads)
 
 Incremental
 -----------
 .. _incremental:
 
 ThinLTO supports fast incremental builds through the use of a cache,
 which currently must be enabled through a linker option.
 
 - gold (as of LLVM 4.0):
   ``-Wl,-plugin-opt,cache-dir=/path/to/cache``
-- ld64 (support in clang 3.9 and Xcode 8):
+- ld64 (supported since clang 3.9 and Xcode 8) and Mach-O ld64.lld (as of LLVM
+  15.0):
   ``-Wl,-cache_path_lto,/path/to/cache``
-- ELF lld (as of LLVM 5.0):
+- ELF ld.lld (as of LLVM 5.0):
   ``-Wl,--thinlto-cache-dir=/path/to/cache``
 - COFF lld-link (as of LLVM 6.0):
   ``/lldltocache:/path/to/cache``
 
 Cache Pruning
 -------------
 
 To help keep the size of the cache under control, ThinLTO supports cache
-pruning. Cache pruning is supported with gold, ld64 and ELF and COFF lld, but
-currently only gold, ELF and COFF lld allow you to control the policy with a
-policy string. The cache policy must be specified with a linker option.
+pruning. Cache pruning is supported with gold, ld64, and lld, but currently only
+gold and lld allow you to control the policy with a policy string. The cache
+policy must be specified with a linker option.
 
 - gold (as of LLVM 6.0):
   ``-Wl,-plugin-opt,cache-policy=POLICY``
-- ELF lld (as of LLVM 5.0):
-  ``-Wl,--thinlto-cache-policy,POLICY``
+- ELF ld.lld (as of LLVM 5.0), Mach-O ld64.lld (as of LLVM 15.0):
+  ``-Wl,--thinlto-cache-policy=POLICY``
 - COFF lld-link (as of LLVM 6.0):
   ``/lldltocachepolicy:POLICY``
 
 A policy string is a series of key-value pairs separated by ``:`` characters.
 Possible key-value pairs are:
 
 - ``cache_size=X%``: The maximum size for the cache directory is ``X`` percent
   of the available space on the disk. Set to 100 to indicate no limit,