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}

## Compiler {#compiler}

## Assembler {#assembler}

In an external link, cmd/link will create a temporary directory, write any
host object files found in package archives to that directory (renamed
to avoid conflicts), write the go.o file to that directory, and invoke
the host linker. The default value for the host linker is $CC, split
into fields, or else "gcc". The specific host linker command line can
be overridden using command line flags: cmd/link -extld=clang

//go:build (ppc64 || ppc64le) && internal

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") }

// license that can be found in the LICENSE file.

package cgotest

// Test that we have no more than one build ID.  In the past we used
// to generate a separate build ID for each package using cgo, and the
// linker concatenated them all.  We don't want that--we only want
// one.

import (
	"bytes"
	"debug/elf"
	"os"
	"testing"
)

func testBuildID(t *testing.T) {
	f, err := elf.Open("/proc/self/exe")

are reserved by the compiler and linker.
</p>

<p>
<code>R10</code> points to the <code>g</code> (goroutine) structure.
Within assembler source code, this pointer must be referred to as <code>g</code>;
the name <code>R10</code> is not recognized.
</p>

<p>
To make it easier for people and compilers to write assembly, the ARM linker

// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build cgo && !windows

// Issue 29563: internal linker fails on duplicate weak symbols.
// No runtime test; just make sure it compiles.

package cgotest

This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.

The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.

      --enable-initfini-array \
      --enable-languages="c,c++" \
      --enable-linker-build-id \
      --enable-plugin \
      --enable-shared \
      --enable-threads=posix \
      --with-default-libstdcxx-abi=${LIBSTDCXX_ABI} \
      --with-gcc-major-version-only \
      --with-linker-hash-style="gnu" \
      && \
      make -j$(nproc) && \
      make install

		if f == nil {
			continue
		}
		fname := f.Name()
		switch fname {
		case "goCallback":
			// TODO(qmuntal): investigate why this function doesn't appear
			// when using the external linker.
			continue
		}
		// In module mode, this package has a fully-qualified import path.
		// Remove it if present.
		fname = strings.TrimPrefix(fname, "cmd/cgo/internal/")
		if !strings.HasPrefix(fname, "test.") {