Fix configure 'major' check causing <sys/sysmacros.h> to miss.

[Explorer09]

A logic mistake in pull request #746 causes <sys/sysmacro.h> to be not included when AC_HEADER_MAJOR (before autoconf-2.70) finds 'major' in <sys/types.h>. Though this would still build htop, it would still bring deprecation warning in systems using glibc 2.25-2.27. Fix the logic and suppress the warning.

Also, include config.h in Process.c for the sake of strengthening the code.

(This should supersede pull request #867. Thanks @wataash for discovering this.)

[natoscott]

Merged here: htop-dev/htop@dab4144