cmd/go: remove special case for prebuilt cgo library cache keys

This was an oversight from CL 452457 that I noticed while
investigating #56889.

This change essentially undoes CL 335409, which is no longer needed
after CL 450739 because we no longer attempt to use cgo by default
when no C compiler is present.

Updates #47257.
Updates #40042.
Updates #47215.

Change-Id: I29c7ce777a9ec7ba5820dc1d836b12a61b86bc37
Reviewed-on: https://go-review.googlesource.com/c/go/+/452677
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Russ Cox <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>

Author: Bryan C. Mills

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

@@ -278,13 +278,8 @@ func (b *Builder) buildActionID(a *Action) cache.ActionID {
 		fmt.Fprintf(h, "CC=%q %q %q %q\n", ccExe, cppflags, cflags, ldflags)
 		// Include the C compiler tool ID so that if the C
 		// compiler changes we rebuild the package.
-		// But don't do that for standard library packages like net,
-		// so that the prebuilt .a files from a Go binary install
-		// don't need to be rebuilt with the local compiler.
-		if !p.Standard {
-			if ccID, _, err := b.gccToolID(ccExe[0], "c"); err == nil {
-				fmt.Fprintf(h, "CC ID=%q\n", ccID)
-			}
+		if ccID, _, err := b.gccToolID(ccExe[0], "c"); err == nil {
+			fmt.Fprintf(h, "CC ID=%q\n", ccID)
 		}
 		if len(p.CXXFiles)+len(p.SwigCXXFiles) > 0 {
 			cxxExe := b.cxxExe()

src/cmd/go/testdata/script/cgo_stale_precompiled.txt

@@ -16,13 +16,21 @@
 go build -x runtime/cgo
 [!short] stderr '[/\\]cgo'$GOEXE'["]? .* -importpath runtime/cgo'
 
-# https://go.dev/issue/47215: a missing $(go env CC) caused the precompiled net to be stale.
-[!GOOS:plan9] env PATH=''  # Guaranteed not to include $(go env CC)!
-[GOOS:plan9] env path=''
-go build -x runtime/cgo
-! stderr '[/\\]cgo'$GOEXE'["]? .* -importpath runtime/cgo'
-
 # https://go.dev/issue/50183: a mismatched GOROOT_FINAL caused net to be stale.
+env oldGOROOT_FINAL=$GOROOT_FINAL
 env GOROOT_FINAL=$WORK${/}goroot
 go build -x runtime/cgo
 ! stderr '[/\\]cgo'$GOEXE'["]? .* -importpath runtime/cgo'
+
+env GOROOT_FINAL=$oldGOROOT_FINAL
+
+# https://go.dev/issue/47215: a missing $(go env CC) caused the precompiled net
+# to be stale. But as of https://go.dev/cl/452457 the precompiled libraries are
+# no longer installed anyway! Since we're requiring a C compiler in order to
+# build and use cgo libraries in the standard library, we should make sure it
+# matches what's in the cache.
+[!abscc] env CGO_ENABLED=1
+[!abscc] [!GOOS:plan9] env PATH=''  # Guaranteed not to include $(go env CC)!
+[!abscc] [GOOS:plan9] env path=''
+[!abscc] ! go build -x runtime/cgo
+[!abscc] stderr 'C compiler .* not found'