Kokoro: Check lint and doxygen

Move the doxygen CMake output from `out/docs` to `<build>/docs`
`out/docs` requires a GN build or manual directory creation.

Fixed: tint:791
Change-Id: If072f962f444a2d60c368d7c38fd1bb4c5b97caf
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50309
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>
diff --git a/Doxyfile b/Doxyfile
index f6fcbb8..028d0ef 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -58,7 +58,7 @@
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = out/docs
+OUTPUT_DIRECTORY       = $(DOXYGEN_OUTPUT_DIRECTORY)
 
 # 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