[ELF] - Linkerscript: implemented filename specification.

Scripts can contain something like:
KEEP (*crtbegin.o(.ctors))

What means that "*crtbegin.o" is a wildcard of file to take the sections from.
This is some kind of opposite to EXCLUDE_FILE and used in FreeBSD script:
https://svnweb.freebsd.org/base/head/sys/conf/ldscript.amd64?revision=284870&view=markup#l122

Patch implements this.

Differential revision: https://reviews.llvm.org/D22852

llvm-svn: 277042
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
index 103be68..5134888 100644
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -84,8 +84,9 @@
 struct InputSectionDescription : BaseCommand {
   InputSectionDescription() : BaseCommand(InputSectionKind) {}
   static bool classof(const BaseCommand *C);
+  StringRef FilePattern;
   std::vector<StringRef> ExcludedFiles;
-  std::vector<StringRef> Patterns;
+  std::vector<StringRef> SectionPatterns;
 };
 
 struct PhdrsCommand {