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
/tests?id=cbf169608c223cdfb8bbd62f82129d5c674ef0a6'>tests</a>/<a href='/guix/log/tests/debug-link.scm?id=cbf169608c223cdfb8bbd62f82129d5c674ef0a6'>debug-link.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/debug-link.scm?id=cbf169608c223cdfb8bbd62f82129d5c674ef0a6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-11-12 23:37:13 +0100'>2018-11-12</span></td><td><a href='/guix/commit/tests/debug-link.scm?id=9ed86fe175c15c819d6d86681c8136ff6bc927c0'>tests: Add 'test-assertm' to (guix tests).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/tests.scm (test-assertm): New macro.
* tests/gexp.scm (test-assertm): Remove.
* tests/profiles.scm (test-assertm): Remove.
* tests/challenge.scm (%store, test-assertm): Remove.
* tests/debug-link.scm (%store, test-assertm): Remove.
* tests/size.scm (%store, test-assertm): Remove.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-08-24 18:01:05 +0200'>2018-08-24</span></td><td><a href='/guix/commit/tests/debug-link.scm?id=93c333895a4e2dc9baabec8ade60d9d2ac0a91e2'>grafts: Add (guix build debug-link) and use it.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/19973&gt;.
Reported by Mark H Weaver &lt;mhw@netris.org&gt;.

* guix/build/debug-link.scm: New file.
* guix/build/graft.scm (%graft-hooks): New variable.
(graft): Add #:hooks and honor it.
* guix/grafts.scm (graft-derivation/shallow): Add (guix build
debug-link) and (guix elf) to #:modules.
* tests/debug-link.scm: New file.
* Makefile.am (MODULES): Add guix/build/debug-link.scm.
(SCM_TESTS): Add tests/debug-link.scm.
</span></span></td><td>Ludovic Courtès</td></tr>