libc: Provide both getpgid and __getpgid symbols
libc: Provide both getpgid and __getpgid symbols

Indeed unistd.h header does export '__getpgid' by default, while
uClibc provide only 'getpgid' implementation. The 'getpgid' symbol
is exported by standard header if __USE_XOPEN_EXTENDED is defined.
This patch alignes uClibc implementation with standard header (matching
with glibc behaviour).

Signed-off-by: Carmelo Amoroso <532378793705a04edd56deb76ad8c0442834d55d@st.com>

joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc