[GOLD] PowerPC tls_get_addr_optimize

This implements the special __tls_get_addr_opt call stub for powerpc
gold that returns __thread variable addresses without actually making
a call to __tls_get_addr in most cases.  Shared libraries that are
loaded at program load time (ie. dlopen is not used) have a known
layout for their __thread variables, and thus DTPMOD64/DPTREL64 pairs
describing those variables can be set up by ld.so for the
__tls_get_addr_opt call stub fast exit.
Ref https://sourceware.org/ml/libc-alpha/2015-03/msg00626.html

I really, really wish I'd used a differently versioned __tls_get_addr
symbol than the base symbol to indicate glibc support for the
optimized call, rather than having glibc export __tls_get_addr_opt.  A
lot of the messing around here, flipping symbols from __tls_get_addr
to __tls_get_addr_opt, is caused by that decision.  About the only
benefit is that a user can see at a glance that their disassembled
code is calling __tls_get_addr via the fancy call stub..  Anyway, we
need references to __tls_get_addr to seem like they were to
__tls_get_addr_opt, and in cases like the tsan interceptor, a
definition of __tls_get_addr to seem like one of __tls_get_addr_opt
as well.  That's the reason for Symbol::clear_in_reg and
Symbol_table::clone, and why symbols are substituted in Scan::global
and other places dealing with dynamic linking.

elfcpp/
	* elfcpp.h (DT_PPC_OPT): Define.
	* powerpc.h (PPC_OPT_TLS): Define.
gold/
	* options.h (tls_get_addr_optimize): New option.
	* symtab.h (Symbol::clear_in_reg, clone): New functions.
	(Sized_symbol::clone): New function.
	(Symbol_table::clone): New function.
	* resolve.cc (Symbol::clone, Sized_symbol::clone): New functions.
	* powerpc.cc (Target_powerpc::has_tls_get_addr_opt_,
	tls_get_addr_, tls_get_addr_opt_): New vars.
	(Target_powerpc::tls_get_addr_opt, tls_get_addr,
	is_tls_get_addr_opt, replace_tls_get_addr,
	set_has_tls_get_addr_opt, stk_linker): New functions.
	(Target_powerpc::Track_tls::maybe_skip_tls_get_addr_call): Add
	target param.  Update callers.  Compare symbols rather than names.
	(Target_powerpc::do_define_standard_symbols): Init tls_get_addr_
	and tls_get_addr_opt_.
	(Target_powerpc::Branch_info::mark_pltcall): Translate tls_get_addr
	sym to tls_get_addr_opt.
	(Target_powerpc::Branch_info::make_stub): Likewise.
	(Stub_table::define_stub_syms): Likewise.
	(Target_powerpc::Scan::global): Likewise.
	(Target_powerpc::Relocate::relocate): Likewise.
	(add_3_12_2, add_3_12_13, bctrl, beqlr, cmpdi_11_0, cmpwi_11_0,
	ld_11_1, ld_11_3, ld_12_3, lwz_11_3, lwz_12_3, mr_0_3, mr_3_0,
	mtlr_11, std_11_1): New constants.
	(Stub_table::eh_frame_added_): Delete.
	(Stub_table::tls_get_addr_opt_bctrl_, plt_fde_len_, plt_fde_): New vars.
	(Stub_table::init_plt_fde): New functions.
	(Stub_table::add_eh_frame, replace_eh_frame): Move definition out
	of line.  Init and use plt_fde_.
	(Stub_table::plt_call_size): Return size for tls_get_addr stub.
	Extract alignment code to..
	(Stub_table::plt_call_align): ..this new function.  Adjust all callers.
	(Stub_table::add_plt_call_entry): Set has_tls_get_addr_opt and
	tls_get_addr_opt_bctrl, and align after that.
	(Stub_table::do_write): Write out tls_get_addr stub.
	(Target_powerpc::do_finalize_sections): Emit DT_PPC_OPT
	PPC_OPT_TLS/PPC64_OPT_TLS bit.
	(Target_powerpc::Relocate::relocate): Don't check for or modify
	nop following bl for tls_get_addr stub.

gold/symtab.h

@@ -329,6 +329,11 @@ class Symbol
   set_in_reg()
   { this->in_reg_ = true; }
 
+  // Forget this symbol was seen in a regular object.
+  void
+  clear_in_reg()
+  { this->in_reg_ = false; }
+
   // Return whether this symbol has been seen in a dynamic object.
   bool
   in_dyn() const
@@ -893,6 +898,13 @@ class Symbol
   set_non_zero_localentry()
   { this->non_zero_localentry_ = true; }
 
+  // Completely override existing symbol.  Everything bar name_,
+  // version_, and is_forced_local_ flag are copied.  version_ is
+  // cleared if from->version_ is clear.  Returns true if this symbol
+  // should be forced local.
+  bool
+  clone(const Symbol* from);
+
  protected:
   // Instances of this class should always be created at a specific
   // size.
@@ -1182,6 +1194,13 @@ class Sized_symbol : public Symbol
   void
   allocate_common(Output_data*, Value_type value);
 
+  // Completely override existing symbol.  Everything bar name_,
+  // version_, and is_forced_local_ flag are copied.  version_ is
+  // cleared if from->version_ is clear.  Returns true if this symbol
+  // should be forced local.
+  bool
+  clone(const Sized_symbol<size>* from);
+
  private:
   Sized_symbol(const Sized_symbol&);
   Sized_symbol& operator=(const Sized_symbol&);
@@ -1687,6 +1706,15 @@ class Symbol_table
   version_script() const
   { return version_script_; }
 
+  // Completely override existing symbol.
+  template<int size>
+  void
+  clone(Sized_symbol<size>* to, const Sized_symbol<size>* from)
+  {
+    if (to->clone(from))
+      this->force_local(to);
+  }
+
  private:
   Symbol_table(const Symbol_table&);
   Symbol_table& operator=(const Symbol_table&);