valgrind: added suppression on optimized code

gcc 4.7.2 with -O2 will optimize Curl_connect by inlining some
functions two levels deep, which makes the valgrind suppression
fail to match. The underlying reason for these idna suppressions is
a gcc strlen optimization when compiling libidn; compiling it with
-fno-builtin-strlen makes this suppression unnecessary.

tests/valgrind.supp

@@ -39,3 +39,19 @@
    fun:operate
    fun:main
 }
+
+{
+   libidn-idna_to_ascii-error-inlined-functions
+   Memcheck:Addr4
+   fun:idna_to_ascii_4z
+   fun:idna_to_ascii_8z
+   fun:idna_to_ascii_lz
+   fun:fix_hostname
+   fun:Curl_connect
+   fun:multi_runsingle
+   fun:curl_multi_perform
+   fun:easy_perform.part.4
+   fun:operate_do
+   fun:operate
+   fun:main
+}