[lld] Remove special cases from default ld driver mode.

[danalbert]

Summary

Use the Gnu driver mode by default for all platforms when ld is
invoked. Other names for the program (such as link or ld64) continue
working as before.

[srhines]

LGTM on the Android side. Thanks Dan for handling this.

[smeenai]

I think this should be fine. While the Darwin linker is indeed called ld as well, anyone who's using LLD for Darwin should be going through the Clang driver with -fuse-ld=lld, which will continue to do the right thing.

[MaskRay]

Thanks!

[ruiu]

LGTM

I think this behavior was carried over from the previous version of lld, but I believe this would cause confusion than being convenient. This is also against our general policy to make cross-linking easier, which is "lld should not change the behavior on which OS it is running".

[thakis]

This breaks tests on mac: http://45.33.8.238/mac/12792/step_10.txt

lld/tools/lld/lld.cpp

for (auto it = expandedArgs.begin(); it + 1 != expandedArgs.end(); ++it) {
     if (StringRef(*it) != "-m")
       continue;
     return isPETargetName(*(it + 1));
   }
   return false;
 }
 
 static Flavor parseProgname(StringRef progname) {
-#if __APPLE__
-  // Use Darwin driver for "ld" on Darwin.
-  if (progname == "ld")
-    return Darwin;
-#endif
-
-#if LLVM_ON_UNIX
-  // Use GNU driver for "ld" on other Unix-like system.
+  // Use GNU driver for "ld" by default.
   if (progname == "ld")
     return Gnu;
-#endif
 
   // Progname may be something like "lld-gnu". Parse it.
   SmallVector<StringRef, 3> v;
   progname.split(v, "-");
   for (StringRef s : v)
     if (Flavor f = getFlavor(s))
       return f;
   return Invalid;