tests: fix critical existence failure of doxygen test

It was totally subproject-unsafe, and setting a super bad example. This
is bad, because doxygen is annoying to get right and we occasionally
tell people to go use our example test case.

There is a fun nuance here, that makes doxygen unpredictably work on
some versions, and fail on others. Specifically, values must be quoted
in doxygen 1.8, but not in doxygen 1.9, or they break -- but only if the
output directory contains spaces. This was "fixed" in commit

ef91bacb7a

which actually caused it to act like an unquoted OUTPUT_DIRECTORY is not
provided at all, and then fixed for real in commit

eb3d1eb5ad

For portability, it is necessary to quote this just to be on the safe
side.

Fixes #11579

test cases/frameworks/14 doxygen/doc/Doxyfile.in

@@ -58,7 +58,7 @@ PROJECT_LOGO           =
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = doc
+OUTPUT_DIRECTORY       = "@TOP_BUILDDIR@/doc"
 
 # If the CREATE_SUBDIRS tag is set to YES then doxygen will create 4096 sub-
 # directories (in 2 levels) under the output directory of each output format and

test cases/frameworks/14 doxygen/doc/meson.build

@@ -1,5 +1,5 @@
-cdata.set('TOP_SRCDIR', meson.source_root())
-cdata.set('TOP_BUILDDIR', meson.build_root())
+cdata.set('TOP_SRCDIR', meson.project_source_root())
+cdata.set('TOP_BUILDDIR', meson.project_build_root())
 
 doxyfile = configure_file(input: 'Doxyfile.in',
                           output: 'Doxyfile',

test cases/frameworks/14 doxygen/meson.build

@@ -1,4 +1,4 @@
-project('doxygen test', 'cpp', version : '0.1.0')
+project('doxygen test', 'cpp', version : '0.1.0', meson_version: '>=0.56')
 
 spede_inc = include_directories('include')