The `-force-single-frontend-invocation` flag predates WMO and is now an
alias for `-whole-module-optimization`. We should use the latter and let
the former fade into history.
Add a new action, LoadModuleJobAction, that the driver can use to schedule a
load of a given module before we fan out and invoke the frontend multiple
times. This gives the module interface loader a chance to compile it from a
module interface before we start with parallel invocations, avoiding starting
potentially dozens of redundant compiles of a large module. Start by using this
on the standard library.
Quick fix for rdar://52839445
Most of the driver tests currently don't work on Windows, but these two were relatively fixable.
- Moved the dsym checks to actions-dsym and ignore that on windows
- alternatively match the full path of dsymutil, which on Windows is
given as "C:\....\dsymutil.exe" verify-debug-info ...
