llvm-config: Print system libraries with --libs instead of --ldflags

[chapuni]

Summary

Although I don't think it'd be *the right way* but more practical than ever.

In trunk, --ldflags prints out -L <dir> and system libs, for example -lpthread.
This behavior is useless and sometimes reported to bugs. (Seek llvm-config in bugs)

I suggest to print system libs after --libs. In fact, almost all system_libs are required from LLVMSupport.
Printing system libs at tail would satisfy most cases.

For example on mingw,

$ bin/llvm-config.exe --ldflags --libs object
-LX:/llvm_objroot/lib
-lLLVMObject -lLLVMSupport -limagehlp -lpsapi -lshell32

My patch affects neither --libnames and --libfiles.

[• ddunbar]

Seems reasonable to me.

llvm/tools/llvm-config/llvm-config.cpp

if (Arg.startswith("-")) {
         OS << ActiveLibDir << '\n';
       } else if (Arg == "--cppflags") {
         OS << ActiveIncludeOption << ' ' << LLVM_CPPFLAGS << '\n';
       } else if (Arg == "--cflags") {
         OS << ActiveIncludeOption << ' ' << LLVM_CFLAGS << '\n';
       } else if (Arg == "--cxxflags") {
         OS << ActiveIncludeOption << ' ' << LLVM_CXXFLAGS << '\n';
       } else if (Arg == "--ldflags") {
-        OS << "-L" << ActiveLibDir << ' ' << LLVM_LDFLAGS
-           << ' ' << LLVM_SYSTEM_LIBS << '\n';
+        OS << "-L" << ActiveLibDir << ' ' << LLVM_LDFLAGS << '\n';
       } else if (Arg == "--libs") {
         PrintLibs = true;
       } else if (Arg == "--libnames") {
         PrintLibNames = true;
       } else if (Arg == "--libfiles") {
         PrintLibFiles = true;
       } else if (Arg == "--components") {
         for (unsigned j = 0; j != array_lengthof(AvailableComponents); ++j) {
for (unsigned i = 0, e = RequiredLibs.size(); i != e; ++i) {
           OS << "-l" << Lib.slice(3, Lib.size()-2);
           continue;
         }
 
         // Otherwise, print the full path.
         OS << ActiveLibDir << '/' << Lib;
       }
     }
+
+    // Assume LLVMSupport depends on system_libs.
+    // FIXME: LLVMBuild may take care of dependencies to system_libs.
+    if (PrintLibs)
+      OS << ' ' << LLVM_SYSTEM_LIBS << '\n';
+
     OS << '\n';
   } else if (!Components.empty()) {
     errs() << "llvm-config: error: components given, but unused\n\n";
     usage();
   }
 
   return 0;
 }