[ELF] --export-dynamic: don't create dynamic sections for non-PIC static links

The CloudABI (removed from Clang Driver) change from
https://reviews.llvm.org/D29982 does not make sense. GNU ld and gold
don't create dynamic sections for a non-PIC static link when
--export-dynamic is specified.

Creating dynamic sections is harmful in this scenario because we would
consider undefined weak symbols preemptible and generate GLOB_DAT
relocations, breaking the expectation that non-PIC static links only
contain IRELATIVE relocations.

In addition, there are other options that export symbols
(--export-dynamic-symbol, --dynamic-list, etc). It does not make sense
to special case --export-dynamic.

Author: MaskRay

lld/ELF/Driver.cpp

@@ -2724,14 +2724,8 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
 
   parseFiles(files, armCmseImpLib);
 
-  // Now that we have every file, we can decide if we will need a
-  // dynamic symbol table.
-  // We need one if we were asked to export dynamic symbols or if we are
-  // producing a shared library.
-  // We also need one if any shared libraries are used and for pie executables
-  // (probably because the dynamic linker needs it).
-  config->hasDynSymTab =
-      !ctx.sharedFiles.empty() || config->isPic || config->exportDynamic;
+  // Create dynamic sections for dynamic linking and static PIE.
+  config->hasDynSymTab = !ctx.sharedFiles.empty() || config->isPic;
 
   script->addScriptReferencedSymbolsToSymTable();
 

lld/test/ELF/static-with-export-dynamic.s

@@ -16,10 +16,11 @@
 # RELOC-NEXT: Offset Info Type Symbol's Value Symbol's Name + Addend
 # RELOC-NEXT: {{.*}} 0000000100000001 R_X86_64_64 0000000000000000 foo + 0
 
-# COMMON:       Symbol table '.dynsym' contains 2 entries:
-# COMMON-NEXT:  Num: Value Size Type Bind Vis Ndx Name
-# COMMON-NEXT:  0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
-# COMMON-NEXT:  1: 0000000000000000 0 NOTYPE WEAK DEFAULT UND foo
+# NORELOC-NOT: Symbol table '.dynsym'
+# RELOC:       Symbol table '.dynsym' contains 2 entries:
+# RELOC-NEXT:  Num: Value Size Type Bind Vis Ndx Name
+# RELOC-NEXT:  0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
+# RELOC-NEXT:  1: 0000000000000000 0 NOTYPE WEAK DEFAULT UND foo
 # COMMON:      Hex dump of section '.data':
 # COMMON-NEXT: {{.*}} 00000000 00000000 
 # COMMON-EMPTY: