unix: Fix mkerrors.sh to do comparison correctly

Bash should use "=" not "-eq" for equality comparison.

Some incorrect comparison operators were missed in:
https://go-review.googlesource.com/c/sys/+/41832

Change-Id: I110968287b7370870301b2fdd2a4ec188f623a39
Reviewed-on: https://go-review.googlesource.com/61770
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/mkerrors.sh

@@ -17,8 +17,8 @@ if test -z "$GOARCH" -o -z "$GOOS"; then
 fi
 
 # Check that we are using the new build system if we should
-if [[ "$GOOS" -eq "linux" ]] && [[ "$GOARCH" != "sparc64" ]]; then
-	if [[ "$GOLANG_SYS_BUILD" -ne "docker" ]]; then
+if [[ "$GOOS" = "linux" ]] && [[ "$GOARCH" != "sparc64" ]]; then
+	if [[ "$GOLANG_SYS_BUILD" != "docker" ]]; then
 		echo 1>&2 "In the new build system, mkerrors should not be called directly."
 		echo 1>&2 "See README.md"
 		exit 1
@@ -27,7 +27,7 @@ fi
 
 CC=${CC:-cc}
 
-if [[ "$GOOS" -eq "solaris" ]]; then
+if [[ "$GOOS" = "solaris" ]]; then
 	# Assumes GNU versions of utilities in PATH.
 	export PATH=/usr/gnu/bin:$PATH
 fi