hvsupport: construct the group regex upfront

The %groups hash contains all the driver types (e.g.
virHypervisorDriver or virSecretDriver).

When searching for all the APIs that are implemented by a driver
of that specific driver type, we keep iterating over the %groups
hash on every line we look at, then matching against the driver type.

This is inefficient because it prevents perl from caching the regex
and it executes the regex once for every driver type, even though
one regex matching excludes all the others, since all the driver types
are different.

Construct the regex containing all the driver types upfront to save
about 6.4s (~98%) of the script execution time.

docs/hvsupport.pl

@@ -207,28 +207,27 @@ foreach my $src (@srcs) {
     open FILE, "<$src" or
         die "cannot read $src: $!";
 
+    my $groups_regex = join("|", keys %groups);
     $ingrp = undef;
     my $impl;
     while (defined($line = <FILE>)) {
         if (!$ingrp) {
-            foreach my $grp (keys %groups) {
-                if ($line =~ /^\s*(?:static\s+)?$grp\s+(\w+)\s*=\s*{/ ||
-                    $line =~ /^\s*(?:static\s+)?$grp\s+NAME\(\w+\)\s*=\s*{/) {
-                    $ingrp = $grp;
-                    $impl = $src;
-
-                    if ($impl =~ m,.*/node_device_(\w+)\.c,) {
-                        $impl = $1;
-                    } else {
-                        $impl =~ s,.*/(\w+?)_((\w+)_)?(\w+)\.c,$1,;
-                    }
-
-                    if ($groups{$ingrp}->{drivers}->{$impl}) {
-                        die "Group $ingrp already contains $impl";
-                    }
-
-                    $groups{$ingrp}->{drivers}->{$impl} = {};
+            if ($line =~ /^\s*(?:static\s+)?($groups_regex)\s+(\w+)\s*=\s*{/ ||
+                $line =~ /^\s*(?:static\s+)?($groups_regex)\s+NAME\(\w+\)\s*=\s*{/) {
+                $ingrp = $1;
+                $impl = $src;
+
+                if ($impl =~ m,.*/node_device_(\w+)\.c,) {
+                    $impl = $1;
+                } else {
+                    $impl =~ s,.*/(\w+?)_((\w+)_)?(\w+)\.c,$1,;
                 }
+
+                if ($groups{$ingrp}->{drivers}->{$impl}) {
+                    die "Group $ingrp already contains $impl";
+                }
+
+                $groups{$ingrp}->{drivers}->{$impl} = {};
             }
 
         } else {