[llvm-config] Fix bug where `--libfiles` and `--names` would produce incorrect output

[delcypher]

Summary

[llvm-config] Fix bug where --libfiles and --names would produce
incorrect output when LLVM is built with LLVM_BUILD_LLVM_DYLIB.

llvm-config previously produced output like this

$ llvm-config --libfiles
/usr/lib/liblibLLVM-4.0svn.so.so
$ llvm-config --libnames
liblibLLVM-4.0svn.so.so

The library prefix and shared library extension were added to
the library name twice which was wrong.

I wanted to write a test cases for this but it looks like all
llvm-config tests were disabled by r260386 so I'll leave this for
now.

[delcypher]

@tstellarAMD If you're still doing the point releases a fix for the problem fixed by this patch should be back ported to LLVM 3.9.x if possible because it also has this bug.

[delcypher]

@beanz @axw @DiamondLovesYou Ping.

[axw]

Sorry for the delay.

[beanz]

@delcypher this patch LGTM. Thank you for mentioning rL260386. I had no idea that patch (or rL260281) had been committed. Neither of those are remotely acceptable, and both need to be fixed. I'll take a look at that today.

[delcypher]

In D27393#620114, @beanz wrote:

@delcypher this patch LGTM. Thank you for mentioning rL260386. I had no idea that patch (or rL260281) had been committed. Neither of those are remotely acceptable, and both need to be fixed. I'll take a look at that today.

@beanz Thanks for approving and please do take a look at those tests. It was rather concerning to me that those tests were disabled in what looked like a short term commit but then were never re-enabled.

[beanz]

I just committed rL289490, which reverts the commit that disabled the tests. They work fine for me (after fixing one), so let's see what happens on the bots.

tools/llvm-config/llvm-config.cpp

auto GetComponentLibraryNameSlice = [&](const StringRef &Lib,
 
     return false;
   };
   /// Maps Unixizms to the host platform.
   auto GetComponentLibraryFileName = [&](const StringRef &Lib,
                                          const bool Shared) {
     std::string LibFileName;
     if (Shared) {
+      if (Lib == DyLibName) {
+        // Treat the DyLibName specially. It is not a component library and
+        // already has the necessary prefix and suffix (e.g. `.so`) added so
+        // just return it unmodified.
+        assert(Lib.endswith(SharedExt) && "DyLib is missing suffix");
+        LibFileName = Lib;
+      } else {
         LibFileName = (SharedPrefix + Lib + "." + SharedExt).str();
+      }
     } else {
       // default to static
       LibFileName = (StaticPrefix + Lib + "." + StaticExt).str();
     }
 
     return LibFileName;
   };
   /// Get the full path for a possibly shared component library.