Hi,

Currently Emacs with native comp will comp .eln file name by the full context of the .el or .el.gz file in function "comp-el-to-eln-rel-filename".
For example, emacs startup will require the simple.elc, then have to read full of simple.el.gz to calculate the name simple-X-Y.eln. 

That's slow on Windows.

This patch introduced a new option "fts" (file time stamp) for "--with-native-compile", it will let the function "comp-el-to-eln-rel-filename" to get the .eln name by reading the .el/.el.gz file timestamp, make emacs faster on Windows. On my Windows testing env, the  Emacs startup up time was reduced from 8s to 6.5s with 386 packages, speedup ~20%.

The option can be combined with the exists option "aot", like "--with-native-compile=aot,fts".

This patch is safe for Emacs Windows release, which building with native compile enabled, but does not ship the libgccjit.dll. So the shipped *.eln is like constant files, user won't be able to recompile one; then this patch is safe for the scenario. 

Please help review this new option. Thanks

Best Regards
Lin