Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

The (%esp & 0xf) == 0 should be true before the call instruction is
executed, for the properly aligned stack.

Reported and tested by: rstone
Pointy hat to: kib
MFC after: 3 days

Add section .note.GNU-stack for assembly files used by 386 and amd64.

Let all .c and .S files under lib/csu consistently use the __FBSDID()
macro for identification, instead of several different hand-rolled
variants (plain .ident, .ascii, etc).

Add unwind annotations to the asm part of crt1 on i386. Terminate the
process with SIGTRAP if _start1() unexpectedly returns.

Reviewed by: kan
MFC after: 2 weeks

Properly support -fPIE by linking PIE binaries with specially-built
Scrt1.o instead of crt1.o, since the later is built as non-PIC.

Separate i386-elf crt1.c into the pure assembler part and C code,
supplying all data extracted by assembler stub as explicit parameters [1].
Hide and localize _start1 symbol used as an interface between asm and
C code.

In collaboration with: kan
Inspired by: PR i386/127387 [1]
Prodded and tested by: rdivacky [1]
MFC after: 3 weeks