please don't use #pragma GCC system_header

[Michael Stahl]

... because it not only disables warnings, it also prevents generating
Makefile dependencies for the file, and that is what caused everybody's
build to break after yesterday's ICU upgrade.

better to use "#pragma GCC diagnostic ignored" which does not have bad
side effects.

if your build currently fails when linking in i18npool or forms you need
to do "make i18npool.clean forms.clean".