build: attempt at reproducible builds (#30321)

This PR implements the conclusions from
#28987 (comment),
that is:

Building with `--strip-all` as a ld-flag to the cgo linker, to remove
symbols. Without that, some spurious reference to a temporary file is
included into the kzg-related library.

Building with `--build-id=none`, to avoid putting a `build id` into the file.

build/ci.go

@@ -249,7 +249,11 @@ func buildFlags(env build.Environment, staticLinking bool, buildTags []string) (
 	if runtime.GOOS == "linux" {
 		// Enforce the stacksize to 8M, which is the case on most platforms apart from
 		// alpine Linux.
-		extld := []string{"-Wl,-z,stack-size=0x800000"}
+		// See https://sourceware.org/binutils/docs-2.23.1/ld/Options.html#Options
+		// regarding the options --build-id=none and --strip-all. It is needed for
+		// reproducible builds; removing references to temporary files in C-land, and
+		// making build-id reproducably absent.
+		extld := []string{"-Wl,-z,stack-size=0x800000,--build-id=none,--strip-all"}
 		if staticLinking {
 			extld = append(extld, "-static")
 			// Under static linking, use of certain glibc features must be