Call tls_get_addr via GOT for GNU TLS if possiblehjl/no-plt/master

There are extensions to x86-64 and i386 psABIs to call tls_get_addr via
GOT.  X86 assembler and linker in binutils 2.27 implemented

call *__tls_get_addr@GOTPCREL(%rip)

in 64-bit and

call *___tls_get_addr@GOT(%reg)

in 32-bit. We check if 32-bit x86 assembler and linker work with

call *___tls_get_addr@GOT(%reg)

as changes for x86-64 assembler and linker were made before 32-bit x86
assembler and linker.

Since any integer register except EAX, which is used to pass parameter
to ___tls_get_addr, and ESP, can be used as GOT base, a new register
class, TLS_REGS, along with a new constraint, Yb, are added, improve
register allocation for dynamic TLS patterns.

gcc/

	* configure.ac (calling ___tls_get_addr via GOT): New
	assembler/linker check.
	(HAVE_AS_IX86_TLS_GET_ADDR_GOT): New.  Defined to 1 if 32-bit
	assembler and linker supports calling ___tls_get_addr via GOT.
	Otherise, defined to 0.
	* config.in: Regenerated.
	* configure: Likewise.
	* config/i386/constraints.md (Yb): New constraint.
	* config/i386/i386.h (reg_class): Add TLS_REGS.
	(REG_CLASS_NAMES): Add TLS_REGS.
	(REG_CLASS_CONTENTS): Likewise.
	* config/i386/i386.md (*tls_global_dynamic_32_gnu): Replace
	the b constraint with the Yb constraint.  Call ___tls_get_addr
	via GOT for GNU TLS with -fno-plt if HAVE_AS_IX86_TLS_GET_ADDR_GOT
	is 1.
	(*tls_local_dynamic_base_32_gnu): Likewise.
	(*tls_global_dynamic_64_<mode>): Call _tls_get_addr via GOT for
	GNU TLS with -fno-plt if HAVE_AS_IX86_TLS_GET_ADDR_GOT is 1.
	(*tls_local_dynamic_base_64_<mode>): Likewise.

gcc/testsuite/

	* gcc.target/i386/noplt-gd-1.c: New test.
	* gcc.target/i386/noplt-gd-2.c: Likewise.
	* gcc.target/i386/noplt-gd-3.c: Likewise.
	* gcc.target/i386/noplt-ld-1.c: Likewise.
	* gcc.target/i386/noplt-ld-2.c: Likewise.
	* gcc.target/i386/noplt-ld-3.c: Likewise.
	* lib/target-supports.exp
	(check_effective_target_tls_get_addr_via_got): New.

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