scripts: kernel-doc: fix typedef support for struct/union parsing

Currently, there are ~1290 occurrences in 447 files in the kernel tree
'typedef struct/union' syntax for defining some struct/union. However,
kernel-doc currently does not support that syntax. Of the ~1290
occurrences, there are four occurrences in ./include/linux/zstd.h with
typedef struct/union syntax and a preceding kernel-doc; all other
occurrences have no preceding kernel-doc.

Add support for parsing struct/union following this syntax.
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
Link: https://lore.kernel.org/r/20210225145033.11431-1-yashsri421@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/kernel-doc

@@ -1201,12 +1201,23 @@ sub dump_union($$) {
 sub dump_struct($$) {
     my $x = shift;
     my $file = shift;
+    my $decl_type;
+    my $members;
+    my $type = qr{struct|union};
+    # For capturing struct/union definition body, i.e. "{members*}qualifiers*"
+    my $definition_body = qr{\{(.*)\}(?:\s*(?:__packed|__aligned|____cacheline_aligned_in_smp|____cacheline_aligned|__attribute__\s*\(\([a-z0-9,_\s\(\)]*\)\)))*};
 
-    if ($x =~ /(struct|union)\s+(\w+)\s*\{(.*)\}(\s*(__packed|__aligned|____cacheline_aligned_in_smp|____cacheline_aligned|__attribute__\s*\(\([a-z0-9,_\s\(\)]*\)\)))*/) {
-	my $decl_type = $1;
+    if ($x =~ /($type)\s+(\w+)\s*$definition_body/) {
+	$decl_type = $1;
 	$declaration_name = $2;
-	my $members = $3;
+	$members = $3;
+    } elsif ($x =~ /typedef\s+($type)\s*$definition_body\s*(\w+)\s*;/) {
+	$decl_type = $1;
+	$declaration_name = $3;
+	$members = $2;
+    }
 
+    if ($members) {
 	if ($identifier ne $declaration_name) {
 	    print STDERR "${file}:$.: warning: expecting prototype for $decl_type $identifier. Prototype was for $decl_type $declaration_name instead\n";
 	    return;