Rewrite the public symbol check to verify the shared libraries, to check for
more things, and to avoid duplication; fixes make check on ARM

Taken from Debian:
https://salsa.debian.org/multimedia-team/mpeg2dec/blob/master/debian/patches/61_global-symbol-test.patch

--- mpeg2dec.orig/test/globals
+++ mpeg2dec/test/globals
@@ -1,4 +1,8 @@
 #!/bin/sh
+# TODO
+# - fix checking of .a libs; problem is that "nm -g --defined-only" lists
+#   internal symbols; this can be solved by using objdump, but it's probably
+#   good enough to just run the tests on the shared lib
 
 if test x"$srcdir" != x""; then
     builddir="."	# running from make check, but it does not define that
@@ -14,22 +18,30 @@ builddir=`cd $builddir;pwd`
 
 error=0
 
-bad_globals=`nm -g --defined-only $builddir/../libmpeg2/*.o |\
-    awk '{if ($3) print $3}' | grep -v '^_\?mpeg2_'`
-
-if test x"$bad_globals" != x""; then
-    echo BAD GLOBAL SYMBOLS:
-    for s in $bad_globals; do echo $s; done
+# check_bad_public_symbols <symbol prefix> <lib file> [<lib file>...]
+#
+# checks public symbols in shared libs:
+# - allow prefix_anything
+# - reject _prefixanything
+# - allow _anything
+# - reject anything else
+#
+# NB: skips missing files
+check_bad_public_symbols() {
+    symbols_prefix="$1"
+    shift
+    lib_files=`ls "$@" 2>/dev/null`
+    [ -z "$lib_files" ] && return
+    bad_globals=`nm -g --defined-only $lib_files |
+        awk '{if ($3) print $3}' |
+        sed -n "/^${symbols_prefix}_/ d; /^_${symbols_prefix}/ { p; d }; /^_/ d; p"`
+    [ -z "$bad_globals" ] && return
     error=1
-fi
-
-bad_globals=`nm -g --defined-only $builddir/../libmpeg2/convert/*.o |\
-    awk '{if ($3) print $3}' | grep -v '^_\?mpeg2convert_'`
+    echo BAD GLOBAL SYMBOLS in $lib_files:
+    echo "$bad_globals"
+}
 
-if test x"$bad_globals" != x""; then
-    echo BAD GLOBAL SYMBOLS:
-    for s in $bad_globals; do echo $s; done
-    error=1
-fi
+check_bad_public_symbols mpeg2 $builddir/../libmpeg2/.libs/libmpeg2.so
+check_bad_public_symbols mpeg2convert $builddir/../libmpeg2/convert/.libs/libmpeg2convert.so
 
 exit $error
66e40ff66dbafc06d48811b2c4ce6'>tests</a>/<a href='/guix/log/tests/offload.scm?id=dc8c3024c0e66e40ff66dbafc06d48811b2c4ce6'>offload.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/offload.scm?id=dc8c3024c0e66e40ff66dbafc06d48811b2c4ce6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-08-25 13:45:27 -0400'>2020-08-25</span></td><td><a href='/guix/commit/tests/offload.scm?id=4b5a6fbc9b754c0ca70d033dd99f17c4f028733a'>offload: Modify the build-machine record to accept multiple systems.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/offload.scm (&lt;build-machine&gt;)[systems]: New field.
[system]: Accessor changed to %build-machine-system.  Default to #f.
* guix/scripts/offload.scm (build-machine-system): Wrap %build-machine-system
with a deprecation warning.
(build-machine-systems): Access the new systems field or fallback to use
build-machine-system, for backward compatibility.
(machine-matches?): Adjust.
* tests/offload.scm: Add tests...
* Makefile.am (SCM_TESTS): ...and register them.
* doc/guix.texi (Daemon Offload Setup): Update doc.
</span></span></td><td>Maxim Cournoyer</td></tr>