find_common_syms: use "grep -E" instead of "egrep"

Newer Linux systems are starting to emit warnings about using "egrep",
and ask that we use "grep -E", instead.

This patch tested on a system as old as RHEL 6; didn't bother checking
a system older than that.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres

config/find_common_syms

@@ -109,7 +109,7 @@ sub object_find {
     # that turns out to be the case, we can try switching to "nm -P", which is
     # supposed to activate the "portable" (yet ugly) format.  It's also unclear
     # at this point how common support for "nm -P" is.
-    open(NM, '-|', "nm '${obj}' 2>/dev/null | egrep '\\s[cC]\\s'");
+    open(NM, '-|', "nm '${obj}' 2>/dev/null | grep -E '\\s[cC]\\s'");
     SYMBOL: while (my $sym_line = <NM>) {
         if (!$all and is_allowlisted($sym_line)) {
             next SYMBOL;