Tmain: Fix make distcheck

[k-takata]

make distcheck sets the source directories readonly. So, temporary files or output files should be written in $BUILDDIR. Otherwise, tests will fail with permission errors.

make distcheck is important when we create a release.

[coveralls]

Coverage increased (+0.008%) to 86.32% when pulling 61ddb9b on k-takata:fix-distcheck into 19df463 on universal-ctags:master.

[codecov-io]

Codecov Report

Merging #2297 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2297      +/-   ##
==========================================
+ Coverage   86.19%   86.19%   +<.01%     
==========================================
  Files         177      177              
  Lines       35852    35852              
==========================================
+ Hits        30901    30904       +3     
+ Misses       4951     4948       -3

Impacted Files	Coverage Δ
main/routines.c	80.97% <0%> (+1.11%)	⬆️

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[k-takata]

Still this error is shown:

ERROR: files left in build directory after distclean:
./optlib/RSpec.c
./optlib/cmake.c
./optlib/ctags-optlib.c
./optlib/elixir.c
./optlib/elm.c
./optlib/gdbinit.c
./optlib/inko.c
./optlib/man.c
./optlib/markdown.c
./optlib/passwd.c
./optlib/pod.c
./optlib/puppetManifest.c
./optlib/qemuhx.c
./optlib/scss.c
./optlib/systemtap.c
./peg/varlink.c
./peg/varlink.h
Makefile:4888: recipe for target 'distcleancheck' failed

[k-takata]

I focus only on Tmain, units and tlib in this PR.
I will create another PR for the issue I wrote above that target 'distcleancheck' fails.

[masatake]

@k-takata, do you use misc/review?
If not, try it. I believe you like it.

It may help you in test case improvements.

If you got a failure in units or tmain, run the script.
You can inspect a test case and its result interactively.

[k-takata]

Oh, I haven't used it. I will try.