[Driver] Define macro __APPLE_EMBEDDED_SIMULATOR__ when option

-m(i|tv|watch)os-simulator-version-min is on the command line.

Previously the driver would treat -m(i|tv|watch)os-simulator-version-min
as an alias of -m(i|tv|watch)os-version-min. This no longer works since
we now need to distinguish between the two options (the latter is used
for iOS running in a VM, for example).

This commit stops making the simulator options the aliases of the OS
options and defines a macro to differentiate between the two groups of
options. 

rdar://problem/28872911

llvm-svn: 297866