MFC r290537,r290540,r290560,r290856,r290871,r291839:

r290537:

Integrate tools/regression/lib/libc/stdio into the FreeBSD test suite
as lib/libc/tests/stdio

- Fix some whitespace
- Convert the testcases to ATF
- Convert "/dev/null" to _PATH_DEVNULL

Sponsored by: EMC / Isilon Storage Division

r290540:

printfloat_test and scanfloat_test need symbols from msun; these are automatically
provided on amd64, but not i386. Add libm to DPADD/LDADD to unbreak the i386
tinderbox

Pointyhat to: ngie
Sponsored by: EMC / Isilon Storage Division

r290560:

Convert print_positional_test over to ATF

Somehow missed in r290537

Sponsored by: EMC / Isilon Storage Division

r290856 (by bapt):

also skip the definition of ':fopen_regular' to avoid the build to fail due to
unused variables defined by ATF macros

r290871:

Disable -Wformat with scanfloat_test when compiling with gcc to avoid a
"use of assignment suppression and length modifier together in scanf format"
warning on line 90 (it's intentional)

Sponsored by: EMC / Isilon Storage Division

r291839:

Initialize errno to 0 in the nul testcase before testing it

For some odd reason stable/10 requires this, otherwise it always fails
the errno == 0 check on line 196.

Sponsored by: EMC / Isilon Storage Division