[RPM] Disable the clang build flag to build Chromium with gcc.

Clang is used as default instead of gcc in Chromium M38, but Chromium
clang does not run in Tizen chroot. Currently, Tizen clang version is
3.1, so it should be upgraded to 3.5.0

This patch allows to build Chromium with gcc for Tizen IVI.

[Bug] https://bugs.tizen.org/jira/browse/TC-1527