Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Eliminate __real__ and __imag__ gccisms.

Use cpack() and the gcc extension __imag__ to implement cimag() and
conj() instead of using expressions like z * I. The latter is bad for
several reasons:

1. It is implemented using arithmetic, which is unnecessary, and can
generate floating point exceptions, contrary to the requirements on
these functions.

2. gcc implements complex multiplication using a formula that breaks
down for infinities, e.g., it gives INFINITY * I == nan + inf I.

Add implementations for cimag{,f,l}, creal{,f,l} and conj{,f,l}. They are
needed for cases where GCC's builtin functions cannot be used and for
compilers that don't know about them.

Approved by: das (mentor)