Move SymbolTable<ELFT>::Sections out of the class.

The list of all input sections was defined in SymbolTable class for a
historical reason. The list itself is not a template. However, because
SymbolTable class is a template, we needed to pass around ELFT to access
the list. This patch moves the list out of the class so that it doesn't
need ELFT.

llvm-svn: 296309
diff --git a/lld/ELF/Target.cpp b/lld/ELF/Target.cpp
index 046b6a2..5476871 100644
--- a/lld/ELF/Target.cpp
+++ b/lld/ELF/Target.cpp
@@ -60,7 +60,7 @@
 static void or32be(uint8_t *P, int32_t V) { write32be(P, read32be(P) | V); }
 
 template <class ELFT> static std::string getErrorLoc(uint8_t *Loc) {
-  for (InputSectionBase *D : Symtab<ELFT>::X->Sections) {
+  for (InputSectionBase *D : InputSections) {
     auto *IS = dyn_cast_or_null<InputSection>(D);
     if (!IS || !IS->OutSec)
       continue;