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
nix/boost?id=7df42d3774778dfbb92e935df720f6eb52965e66'>boost</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/nix/boost?id=7df42d3774778dfbb92e935df720f6eb52965e66&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-06-24 19:55:22 +0100'>2020-06-24</span></td><td><a href='/guix/commit/nix/boost?id=cd43b55da7ab51c996a7a3449c78f2a493616106'>nix: Tweak .gitignore files.</a><span class='msg-avail'>...<span class='msg-tooltip'>Remove .gitignore entries where they match source files that are tracked in
Git.  This is relevant to me at least, as some code searching tools use
.gitignore files and will ignore matched files.
</span></span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2019-11-26 00:16:36 +0100'>2019-11-26</span></td><td><a href='/guix/commit/nix/boost?id=3a4d5ddd322c7daf0a8c83ca2c87c3fc38b19f0b'>daemon: boost::format: Fix typo "referred".</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/boost/format/exceptions.hpp (too_few_args): Fix typo.
  (too_many_args): Fix typo.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Vagrant Cascadian</td></tr>