Per previous failure of buildfarm member koi (which is no longer
failing, alas).

them after the fact.  This is a more elegant fix for bug #5595.

These are just cosmetic and don't seem worth back-patching far.
I put them into 9.0 just because it was trivial to do so.

build tree.  If we actually build the docs in the VPATH tree, those dirs
will get created then; but if they're present and empty, they capture the
vpathsearch searches in "make install", preventing installation of prebuilt
docs that might exist in the source tree.  Per bug #5595 from Dmtiriy Igrishin.
Fix based on idea from Peter Eisentraut.

from Ian Lance Taylor

(partially) from Ian Lance Taylor

Recode test for equality of source and build directory using 'test -ef',
because even using pwd you might not get equal strings.  Thanks, QNX.

source directory.  This involves mostly makefiles using $(srcdir) when they
might have used ".".  (Regression tests don't work with this, yet.)

Sort out usage of CPPFLAGS, CFLAGS (and CXXFLAGS).  Add "override" keyword
in most places, to preserve necessary flags even when the user overrode the
flags.