c: Do not ignore some forms of -Wimplicit-int in system headers
Most -Wimplicit-int warnings were unconditionally disabled for system
headers. Only missing types for parameters in old-style function
definitions resulted in warnings. This is inconsistent with the
treatment of other permerrors, which are active in system headers.
gcc/c/
* c-decl.cc (grokdeclarator): Do not skip -Wimplicit-int
warnings or errors in system headers.
gcc/testsuite/
* gcc.dg/permerror-system.c: Expect all -Wimplicit-int
permerrors.