Overridable nm (variable NM) in configuration

From David Siefert (soap@gentoo.org):

we're currently running smoke checks in Gentoo for smoking out implicit
dependencies on unprefixed/non-overridable toolchain calls in build
systems. We found that libcdio has naked "nm" calls:
https://bugs.gentoo.org/719064

configure.ac

@@ -89,6 +89,9 @@ AC_PROG_MKDIR_P
 AC_PROG_AWK
 AC_SUBST(AWK)
 
+AC_ARG_VAR([NM], [utility for listing symbols from object files])
+AC_CHECK_TOOL([NM], [nm])
+
 if test "x$GCC" != "xyes"
 then
   AC_MSG_WARN([

lib/cdda_interface/Makefile.am

@@ -133,8 +133,8 @@ libcdio_cdda.la.ver: $(libcdio_cdda_la_OBJECTS) $(srcdir)/libcdio_cdda.sym
 	echo 'CDIO_CDDA_$(libcdio_cdda_la_MAJOR) { ' > $@
 	objs=`for obj in $(libcdio_cdda_la_OBJECTS); do sed -ne "s/^pic_object='\(.*\)'$$/\1/p" $$obj; done`; \
 	if test -n "$$objs" ; then \
-	  nm $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_cdda.sym; then if test $$first = true; then echo "  global:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
-	  nm $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_cdda.sym; then :; else if test $$first = true; then echo "  local:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
+	  ${NM} $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_cdda.sym; then if test $$first = true; then echo "  global:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
+	  ${NM} $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_cdda.sym; then :; else if test $$first = true; then echo "  local:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
 	fi
 	echo '};' >> $@
 else !BUILD_VERSIONED_LIBS

lib/paranoia/Makefile.am

@@ -146,8 +146,8 @@ libcdio_paranoia.la.ver: $(libcdio_paranoia_la_OBJECTS) $(srcdir)/libcdio_parano
 	echo 'CDIO_PARANOIA_$(libcdio_paranoia_la_MAJOR) { ' > $@
 	objs=`for obj in $(libcdio_paranoia_la_OBJECTS); do sed -ne "s/^pic_object='\(.*\)'$$/\1/p" $$obj; done`; \
 	if test -n "$$objs" ; then \
-	  nm $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_paranoia.sym; then if test $$first = true; then echo "  global:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
-	  nm $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_paranoia.sym; then :; else if test $$first = true; then echo "  local:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
+	  ${NM} $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_paranoia.sym; then if test $$first = true; then echo "  global:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
+	  ${NM} $${objs} | sed -n -e 's/^.*[ 	][ABCDGIRSTW][ABCDGIRSTW]*[ 	][ 	]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libcdio_paranoia.sym; then :; else if test $$first = true; then echo "  local:"; first=false; fi; echo "    $${symbol};"; fi; done; } >> $@; \
 	fi
 	echo '};' >> $@
 else