Build armv7s for iOS, use architecture names in paths

Up to now we've been assuming that we have only one 32-bit target and
one 64-bit target per platform. There is a need to be able to build
armv7s for iOS, but assumptions abound in the organization of files per
architecture - tests, cmake targets, and installation.

- Build armv7s when building for iOS
- Use the actual architecture name, not blank or "/32" in all paths
  related to architecture.

Testing: Clean buildbot incremental RA tests pass (requires a test
update in SourceKit as well).

rdar://problem/20206215

Swift SVN r26600

lib/Frontend/CompilerInvocation.cpp

@@ -46,8 +46,7 @@ static void updateRuntimeLibraryPath(SearchPathOptions &SearchPathOpts,
   llvm::sys::path::append(LibPath, getPlatformNameForTriple(Triple));
   SearchPathOpts.RuntimeLibraryPath = LibPath.str();
 
-  if (Triple.isArch32Bit())
-    llvm::sys::path::append(LibPath, "32");
+  llvm::sys::path::append(LibPath, Triple.getArchName());
   SearchPathOpts.RuntimeLibraryImportPath = LibPath.str();
 }