ENH: implement variables substitution in configuration #2075

Job	Run time
msvc (3.11)	4m 31s
mypy	38s
cygwin (3.9)	9m 47s
homebrew (3.8)	3m 49s
homebrew (3.11)	4m 18s
pyston (3.8)	2m 11s
test (ubuntu, 3.7)	1m 48s
test (ubuntu, 3.11)	2m 28s
test (macos, 3.7)	3m 47s
test (macos, 3.11)	3m 46s
test (windows, 3.7)	7m 53s
test (windows, 3.11)	6m 41s
test (ubuntu, pypy-3.9)	5m 35s
test (ubuntu, 3.8)	2m 0s
test (ubuntu, 3.9)	2m 57s
test (ubuntu, 3.10)	2m 22s
test (ubuntu, 3.12-dev)	3m 12s
test (ubuntu, 3.11, ~=0.63.3)	2m 21s
test (ubuntu, 3.11, ~=0.64.0)	2m 15s
test (ubuntu, 3.11, ~=1.0.0)	2m 57s
test (ubuntu, 3.11, ~=1.1.0)	2m 30s
test (ubuntu, 3.11, @git+https://github.com/mesonbuild/meson.git)	2m 24s
test (windows, 3.11, @git+https://github.com/mesonbuild/meson.git)	10m 31s
	1h 30m 41s

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