pmix2x: common syms: whitelist bison-generated common symbols

Bison generates some common symbols that we can't do anything about,
so whitelist them.

opal/mca/pmix/pmix2x/common_sym_whitelist.txt

@@ -0,0 +1,6 @@
+# Ignore symbols in this component that are auto-generated and we
+# can't do anything about them (e.g., flex/bison symbols).
+pmix_util_keyval_yyleng
+pmix_util_keyval_yytext
+pmix_show_help_yyleng
+pmix_show_help_yytext