Introduce an option to omit needless words when importing from Clang.

The -enable-omit-needless-words option attempts to omit needless words
from method names imported from Clang. Broadly speaking, a word is
needless if it merely restates the type of the corresponding parameter,
using reverse camel-case matching of the type name to the
function/parameter name. The word "With" is also considered needless
if whether follows it is needless, e.g.,

  func copyWithZone(zone: NSZone)

gets reduced to

  func copy(zone: NSZone)

because "Zone" merely restates type information and the remaining,
trailing "With" is also needless.

There are some special type naming rules for builtin Objective-C types,
e.g.,

  id -> "Object"
  SEL -> "Selector"
  Block pointer types -> "Block"

as well as some very-Cocoa-specific matching rules, e.g., the type
"IndexSet" matches the name "Indexes" or "Indices".

Expect a lot of churn with these heuristics; this is part of
rdar://problem/22232287.

Swift SVN r31178

lib/Frontend/CompilerInvocation.cpp

@@ -782,6 +782,8 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts,
   Opts.InferImplicitProperties |=
     Args.hasArg(OPT_enable_objc_implicit_properties);
 
+  Opts.OmitNeedlessWords |= Args.hasArg(OPT_enable_omit_needless_words);
+
   Opts.DumpClangDiagnostics |= Args.hasArg(OPT_dump_clang_diagnostics);
 
   if (Args.hasArg(OPT_embed_bitcode))