Reland "[llvm][Support] Add support for executing a detached process (#81708)" (#83367)

Relands #81708, which was reverted by
f410f74c, now with a corrected unit
test. Origionally the test failed on Windows when run with lit as
`GetConsoleWindow` could not retrieve a window handle regardless of
whether `DetachProcess` was `true` or `false`. The test now uses
`GetStdHandle(STD_OUTPUT_HANDLE)` which does not rely on a console
window existing. Original commit message below.

Adds a new parameter, `bool DetachProcess` with a default option of
`false`, to `llvm::sys::ExecuteNoWait`, which, when set to `true`,
executes the specified program without a controlling terminal.

Functionality added so that the module build daemon can be run without a
controlling terminal.