Factor out static members from DefinedRegular.

This patch moves statically-allocated Elf_Sym objects out
of DefinedRegular class, so that the class definition becomes
smaller.

llvm-svn: 256408
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 9402c2d..6d88137 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -279,7 +279,7 @@
     // so that it points to an absolute address which is relative to GOT.
     // See "Global Data Symbols" in Chapter 6 in the following document:
     // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
-    Symtab.addAbsolute("_gp", DefinedRegular<ELFT>::MipsGp);
+    Symtab.addAbsolute("_gp", ElfSym<ELFT>::MipsGp);
   }
 
   for (std::unique_ptr<InputFile> &F : Files)