build: allow passing multiple libs to pkg_config

Sometimes it's necessary to pass multiple library names to pkg-config,
e.g. the brotli shared libraries can be pulled in with
    pkg-config libbrotlienc libbrotlidec

Update the code to handle both, strings (as used so far), and lists
of strings.

Signed-off-by: André Draszik <git@andred.net>

PR-URL: #32046
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

configure.py

@@ -680,7 +680,11 @@ def pkg_config(pkg):
   retval = ()
   for flag in ['--libs-only-l', '--cflags-only-I',
                '--libs-only-L', '--modversion']:
-    args += [flag, pkg]
+    args += [flag]
+    if isinstance(pkg, list):
+      args += pkg
+    else:
+      args += [pkg]
     try:
       proc = subprocess.Popen(shlex.split(pkg_config) + args,
                               stdout=subprocess.PIPE)