ELF2: LinkerScript: Interpret -l and = file name prefixes.

In the linker script, -l and = have the same meaning as in the command line.
In addition to that, if a path is not absolute, the path needs to be searched
from the search paths. This patch implements them.

llvm-svn: 249967
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 293551c..89b0d83 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -38,7 +38,7 @@
   llvm::StringRef SoName;
   llvm::StringRef Sysroot;
   std::string RPath;
-  std::vector<llvm::StringRef> InputSearchPaths;
+  std::vector<llvm::StringRef> SearchPaths;
   bool AllowMultipleDefinition;
   bool DiscardAll;
   bool DiscardLocals;