patch.bbclass: Use one TMPDIR per patching process

patch.bbclass: Use one TMPDIR per patching process

We must use one TMPDIR per process (/tmp/${PID}) so that the patching
processes don't generate the same temp file name (the "patch" program
uses the TMPDIR environment variable for deciding where to create the
temp files).

[YOCTO #3070]

(From OE-Core rev: 16dbf505c4fdd9fe1820d950ab05c8ea99ad7505)

Signed-off-by: Constantin Musca <constantinx.musca@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>