If lld binary is named "ld" on darwin system, use darwin driver

[kledzik]

Summary

To start qualifying lld for iOS and MacOSX, we'd like to make a drop in replacement for /usr/bin/ld (which is now buried inside Xcode.app). But the existing lld is not a drop in replacement because it requires "-flavor darwin" and the thousands of existing projects don't know to add that. We also cannot rename the lld binary to have "darwin" in the name (which the universal driver and pick up on) because existing projects invoke "ld".

My revised proposal is to check if the binary is named "ld" and was built on a darwin system, if so, use darwin driver.

[ruiu]

I'm OK with this approach, but the other approach would be to
make "ld" smarter. The name "ld" is currently mapped to gnu_ld
but it's deprecated, so we can replace it with a dispatcher which
dispatch according to the system -- to darwin if compiled for Darwin
and gnu_ld for other Unices. Then you don't need to rename
lld-drawin to ld when installing.

[ruiu]

LGTM

[kledzik]

committed in r217112

lib/Driver/UniversalDriver.cpp

       .Case("lld-link", Flavor::win_link)
       .Case("darwin", Flavor::darwin_ld)
       .Case("core", Flavor::core)
-      .Case("ld", Flavor::gnu_ld) // deprecated
+#if __APPLE__
+      // On a Darwin systems, if linker binary is named "ld", use Darwin driver.
+      .Case("ld", Flavor::darwin_ld)
+#else
+      // On other *nix systems, if linker binary is named "ld", use gnu driver.
+      .Case("ld", Flavor::gnu_ld)
+#endif
       .Default(Flavor::invalid);
 }