pgrep: optimize command name copying

strncpy() implementations in glibc and musl use memset() to zero the entire destination string past the source string length. This is hot code path that runs per PID. It makes strncpy() take more cycles than anything else.

Use memccpy() instead since it never touches the destination past the string terminator.

Signed-off-by: Baruch Siach baruch.siach@siklu.com