cmd/cgo: don't generate random numbers for symbols

If cgo is built with -flto the symbols in runtime/cgo is going to
include random numbers which would make builds unreproducible.

Settings -frandom-seeds ensures this is consistent across builds.

    $ strings --all --bytes=8 $WORK/b055/_pkg_.a | grep "gnu.lto_.profile"
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1
    .gnu.lto_.profile.1

Signed-off-by: Morten Linderud <[email protected]>

Author: Foxboron

src/cmd/go/internal/work/exec.go

@@ -2551,6 +2551,12 @@ func (b *Builder) compilerCmd(compiler []string, incdir, workdir string) []strin
 		a = append(a, "-gno-record-gcc-switches")
 	}
 
+	// Tell gcc to not insert truly random numbers into the build process
+	// this ensures LTO won't create random symbols.
+	if b.gccSupportsFlag(compiler, "-frandom-seed=1") {
+		a = append(a, "-frandom-seed=1")
+	}
+
 	// On OS X, some of the compilers behave as if -fno-common
 	// is always set, and the Mach-O linker in 6l/8l assumes this.
 	// See https://golang.org/issue/3253.