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
ut type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=ef30dc4c3698ac0c1a33efde2c59bee7001d7854&amp;showmsg=1'>root</a>/<a href='/guix/log/gnu?id=ef30dc4c3698ac0c1a33efde2c59bee7001d7854&amp;showmsg=1'>gnu</a>/<a href='/guix/log/gnu/installer?id=ef30dc4c3698ac0c1a33efde2c59bee7001d7854&amp;showmsg=1'>installer</a>/<a href='/guix/log/gnu/installer/substitutes.scm?id=ef30dc4c3698ac0c1a33efde2c59bee7001d7854&amp;showmsg=1'>substitutes.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/gnu/installer/substitutes.scm?id=ef30dc4c3698ac0c1a33efde2c59bee7001d7854'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2020-12-11 21:37:07 +0100'>2020-12-11</span></td><td class='logsubject'><a href='/guix/commit/gnu/installer/substitutes.scm?id=8361817bf693742757b096468198626f297bb09e'>install: Discover local substitute servers.</a></td><td>Mathieu Othacehe</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/installer/substitutes.scm: New file.
* gnu/installer/newt/substitutes.scm: New file.
* gnu/local.mk (INSTALLER_MODULES): Add them.
* po/guix/POTFILES.in: Add gnu/installer/newt/substitutes.scm.
* gnu/installer/proxy.scm (with-silent-shepherd): Move to ...
* gnu/installer/utils.scm: ... here.
* gnu/installer/record.scm (&lt;installer&gt;)[substitutes-page]: New field.
* gnu/installer/newt.scm (substitutes-page): New procedure,
(newt-installer): register it.
* gnu/installer.scm (installer-steps): Add "substitutes-page" step.
* gnu/system/install.scm (%installation-services): Add avahi-service-type and
enable substitute server discover in guix-service-type.
[&lt;name-service-switch&gt;]: Set it to %mdns-host-lookup-nss.


</td></tr>