make configure check for visibility preinclude compatible with pcc

pcc does not search for -include relative to the working directory
unless -I. is used. rather than adding -I., which could be problematic
if there's extra junk in the top-level directory, switch back to the
old method (reverting commit 60ed988fd6c67b489d7cc186ecaa9db4e5c25b8c)
of using -include vis.h and relying on -I./src/internal being present
on the command line (which the Makefile guarantees). to fix the
breakage that was present in trycppif checks with the old method,
$CFLAGS_AUTO is removed from the command line passed to trycppif; this
is valid since $CFLAGS_AUTO should not contain options that alter
compiler semantics or ABI, only optimizations, warnings, etc.