syscall: don't assume we have a GETEUID system call

On Alpha GNU/Linux there is no geteuid system call, there is only
    getresuid.  The raw geteuid system call is only used for testing, so
    just skip the test if it's not available.
    
    Reviewed-on: https://go-review.googlesource.com/137655

From-SVN: r264647

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-e7b98cf0a380eb45791cd5c52897224a686dcdec
+944784a93cf89d3a238e5607c993ea5f18f99c12
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/syscall/syscall_linux_test.go

@@ -302,6 +302,10 @@ func TestSyscallNoError(t *testing.T) {
 		t.Skip("skipping root only test")
 	}
 
+	if syscall.Sys_GETEUID == 0 {
+		t.Skip("skipping because there is no geteuid system call")
+	}
+
 	// Copy the test binary to a location that a non-root user can read/execute
 	// after we drop privileges
 	tempDir, err := ioutil.TempDir("", "TestSyscallNoError")

libgo/mksysinfo.sh

@@ -138,6 +138,12 @@ if ! grep '^const SYS_GETDENTS64 ' ${OUT} >/dev/null 2>&1; then
   echo "const SYS_GETDENTS64 = 0" >> ${OUT}
 fi
 
+# The syscall package wants the geteuid system call number.  It isn't
+# defined on Alpha, which only provides the getresuid system call.
+if ! grep '^const SYS_GETEUID ' ${OUT} >/dev/null 2>&1; then
+  echo "const SYS_GETEUID = 0" >> ${OUT}
+fi
+
 # Stat constants.
 grep '^const _S_' gen-sysinfo.go | \
   sed -e 's/^\(const \)_\(S_[^= ]*\)\(.*\)$/\1\2 = _\2/' >> ${OUT}