checkpatch: skip warnings for symbol links

If there is a symbol link in the given patch, checkpatch.pl reports two
inaccurate warnings:

$ cat 0001-selftests-bpf-Add-mptcp-pm_nl_ctl-link.patch

 ... ...

 '''
 # diff --git a/tools/testing/selftests/bpf/mptcp_pm_nl_ctl.c \
 #            b/tools/testing/selftests/bpf/mptcp_pm_nl_ctl.c
 # new file mode 120000
 # index 000000000000..5a08c255b278
 # --- /dev/null
 # +++ b/tools/testing/selftests/bpf/mptcp_pm_nl_ctl.c
 # @@ -0,0 +1 @@
 # +../net/mptcp/pm_nl_ctl.c
 # \ No newline at end of file
 '''

$ ./scripts/checkpatch.pl 0001-selftests-bpf-Add-mptcp-pm_nl_ctl-link.patch

 '''
 WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
 torvalds#57: FILE: tools/testing/selftests/bpf/mptcp_pm_nl_ctl.c:1:
 +../net/mptcp/pm_nl_ctl.c

 WARNING: adding a line without newline at end of file
 torvalds#57: FILE: tools/testing/selftests/bpf/mptcp_pm_nl_ctl.c:1:
 +../net/mptcp/pm_nl_ctl.c

 total: 0 errors, 2 warnings, 16 lines checked
 '''

This patch fixes this by adding a new variable $symbol_link in checkpatch
script, set it if the new file mode is 120000. Skip these two checks
"missing SPDX-License-Identifier" and "adding a line without newline at
end of file" if this variable is set.

Signed-off-by: Geliang Tang <[email protected]>

scripts/checkpatch.pl

@@ -436,6 +436,7 @@ sub hash_show_words {
 }
 
 my $rpt_cleaners = 0;
+my $symbol_link = 0;
 
 if ($terse) {
 	$emacs = 1;
@@ -3595,6 +3596,10 @@ sub process {
 				      "Do not include the paragraph about writing to the Free Software Foundation's mailing address from the sample GPL notice. The FSF has changed addresses in the past, and may do so again. Linux already includes a copy of the GPL.\n" . $herevet)
 		}
 
+		if ($line =~ /^new file mode 120000$/) {
+			$symbol_link = 1;
+		}
+
 # check for Kconfig help text having a real description
 # Only applies when adding the entry originally, after that we do not have
 # sufficient context to determine whether it is indeed long enough.
@@ -3756,7 +3761,8 @@ sub process {
 				}
 
 				if ($comment !~ /^$/ &&
-				    $rawline !~ m@^\+\Q$comment\E SPDX-License-Identifier: @) {
+				    $rawline !~ m@^\+\Q$comment\E SPDX-License-Identifier: @ &&
+				    $symbol_link =~ 1) {
 					WARN("SPDX_LICENSE_TAG",
 					     "Missing or malformed SPDX-License-Identifier tag in line $checklicenseline\n" . $herecurr);
 				} elsif ($rawline =~ /(SPDX-License-Identifier: .*)/) {
@@ -3867,7 +3873,8 @@ sub process {
 		}
 
 # check for adding lines without a newline.
-		if ($line =~ /^\+/ && defined $lines[$linenr] && $lines[$linenr] =~ /^\\ No newline at end of file/) {
+		if ($line =~ /^\+/ && defined $lines[$linenr] && $lines[$linenr] =~ /^\\ No newline at end of file/ &&
+		    $symbol_link =~ 1) {
 			if (WARN("MISSING_EOF_NEWLINE",
 			         "adding a line without newline at end of file\n" . $herecurr) &&
 			    $fix) {