Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

## Assembler {#assembler}

package cgotest

import "testing"

// If gcc is used, and linking internally, __mulsc3 and __muldc3
// will be linked in from libgcc which make several R_PPC64_TOC16_DS
// relocations which may not be resolvable with the internal linker.
func test8694(t *testing.T) { t.Skip("not supported on ppc64/ppc64le with internal linking") }

	JMP	2(PC)					// 6f008000
	JMP	(X5)					// 67800200
	JMP	4(X5)					// 67804200

	// CALL and JMP to symbol are encoded as JAL (using LR or ZERO
	// respectively), with a R_RISCV_JAL relocation. The linker resolves
	// the real address and updates the immediate, using a trampoline in
	// the case where the address is not directly reachable.
	CALL	asmtest(SB)				// ef000000
	JMP	asmtest(SB)				// 6f000000

pkg syscall (freebsd-386-cgo), func SetsockoptInet4Addr(int, int, int, [4]uint8) error
pkg syscall (freebsd-386-cgo), func SetsockoptInt(int, int, int, int) error
pkg syscall (freebsd-386-cgo), func SetsockoptLinger(int, int, int, *Linger) error
pkg syscall (freebsd-386-cgo), func SetsockoptString(int, int, int, string) error
pkg syscall (freebsd-386-cgo), func SetsockoptTimeval(int, int, int, *Timeval) error

	directoryEndSignature    = 0x06054b50
	directory64LocSignature  = 0x07064b50
	directory64EndSignature  = 0x06064b50
	dataDescriptorSignature  = 0x08074b50 // de-facto standard; required by OS X Finder
	fileHeaderLen            = 30         // + filename + extra
	directoryHeaderLen       = 46         // + filename + extra + comment
	directoryEndLen          = 22         // + comment

pkg image/png, type UnsupportedError string
pkg index/suffixarray, func New([]uint8) *Index
pkg index/suffixarray, method (*Index) Bytes() []uint8
pkg index/suffixarray, method (*Index) FindAllIndex(*regexp.Regexp, int) [][]int
pkg index/suffixarray, method (*Index) Lookup([]uint8, int) []int
pkg index/suffixarray, method (*Index) Read(io.Reader) error
pkg index/suffixarray, method (*Index) Write(io.Writer) error

  heuristics; see <a href="https://go.dev/issue/61502">issue #61502</a> for
  more info and to provide feedback.
</p>

<h2 id="linker">Linker</h2>

<p><!-- CL 493136 -->
  The linker's <code>-s</code> and <code>-w</code> flags are now behave more
  consistently across all platforms.
  The <code>-w</code> flag suppresses DWARF debug information generation.

If xxx is data, cgo arranges for C.xxx to refer to the C variable,
with the type translated as described above.  To do this, cgo must
introduce a Go variable that points at the C variable (the linker can
be told to initialize this pointer).  For example, if the gmp library
provided

	mpz_t zero;

then cgo would rewrite a reference to C.zero by introducing

	var _C_zero *C.mpz_t