ELF: Allow -e <entry> with -shared

It is reasonable to specify an entry point for shared objects - for
example, for the FreeBSD rtld ld-elf.so.1.

Unlike GNU ld we leave the entry address as 0 if -shared is specified
without -e.

Differential Revision:	http://reviews.llvm.org/D15454

llvm-svn: 255349
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 2f1cf9b..f1e1abe 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -248,11 +248,6 @@
     if (Config->Entry.empty())
       Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
 
-    // Set either EntryAddr (if S is a number) or EntrySym (otherwise).
-    StringRef S = Config->Entry;
-    if (S.getAsInteger(0, Config->EntryAddr))
-      Config->EntrySym = Symtab.addUndefined(S);
-
     // In the assembly for 32 bit x86 the _GLOBAL_OFFSET_TABLE_ symbol
     // is magical and is used to produce a R_386_GOTPC relocation.
     // The R_386_GOTPC relocation value doesn't actually depend on the
@@ -268,6 +263,13 @@
     Symtab.addIgnoredSym("_GLOBAL_OFFSET_TABLE_");
   }
 
+  if (!Config->Entry.empty()) {
+    // Set either EntryAddr (if S is a number) or EntrySym (otherwise).
+    StringRef S = Config->Entry;
+    if (S.getAsInteger(0, Config->EntryAddr))
+      Config->EntrySym = Symtab.addUndefined(S);
+  }
+
   // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
   // so that it points to an absolute address which is relative to GOT.
   // See "Global Data Symbols" in Chapter 6 in the following document: