ci: gcov: "merge mismatch" errors

[blueyed]

This issue is meant to track "merge mismatch" errors due to using gcov.

With https://travis-ci.org/neovim/neovim/jobs/550297606 (restarted) "merge mismatch" errors showed up:

profiling:/home/travis/build/neovim/neovim/build/src/nvim/CMakeFiles/nvim.dir/fileio.c.gcda:Merge mismatch for function 48

edit: Restarting it then worked - so likely not a ccache issue.

I will try clearing the ccache with gcov jobs, to ensure it is not causing problems in this regard.

https://travis-ci.org/neovim/neovim/jobs/553494382:

profiling:/home/travis/build/neovim/neovim/build/src/nvim/CMakeFiles/nvim.dir/shada.c.gcda:Merge mismatch for function 5

[blueyed]

After #10404:

Travis

Not via GCOV_ERROR_FILE (!?)...

https://travis-ci.org/neovim/neovim/jobs/555720182

build/src/nvim/CMakeFiles/nvim.dir/ops.c.gcda:Merge mismatch for function 62

https://travis-ci.org/neovim/neovim/jobs/555885437

build/src/nvim/CMakeFiles/nvim.dir/eval.c.gcda:Merge mismatch for function 62

https://travis-ci.org/neovim/neovim/jobs/555023022:

[----------] Running tests from /home/travis/build/neovim/neovim/test/functional/core/startup_spec.lua
[ RUN      ] startup pipe at both ends: has("ttyin")==0 has("ttyout")==0: 19.24 ms OK
[ RUN      ] startup with --embed: has("ttyin")==0 has("ttyout")==0: 14.28 ms OK
[ RUN      ] startup in a TTY: has("ttyin")==1 has("ttyout")==1: 33.93 ms OK
[ RUN      ] startup output to pipe: has("ttyin")==1 has("ttyout")==0: 31.74 ms OK
[ RUN      ] startup input from pipe: has("ttyin")==0 has("ttyout")==1: 35.04 ms OK
[ RUN      ] startup input from pipe (implicit) #7679: ERR
test/functional/ui/screen.lua:554: Row 1 did not match.
Expected:
  |*^foo                      |
  |~                        |
  |0 1                      |
  |                         |
Actual:
  |*^profiling:/home/travis/bu|
  |ild/neovim/neovim/build/s|
  |rc/nvim/CMakeFiles/nvim.d|
  |                         |
To print the expect() call that would assert the current screen state, use
screen:snapshot_util(). In case of non-deterministic failures, use
screen:redraw_debug() to show all intermediate screen states.  
stack traceback:
	test/functional/ui/screen.lua:554: in function '_wait'
	test/functional/ui/screen.lua:366: in function 'expect'
	...uild/neovim/neovim/test/functional/core/startup_spec.lua:111: in function <...uild/neovim/neovim/test/functional/core/startup_spec.lua:99>
[ RUN      ] startup input from pipe + file args #7679: FAIL
...uild/neovim/neovim/test/functional/core/startup_spec.lua:119: Expected objects to be the same.
Passed in:
(string) 'ohyeah
0 0 bufs=3profiling:/home/travis/build/neovim/neovim/build/src/nvim/CMakeFiles/nvim.dir/eval.c.gcda:Merge mismatch for function 488
'
Expected:
(string) 'ohyeah
0 0 bufs=3'
stack traceback:
	...uild/neovim/neovim/test/functional/core/startup_spec.lua:119: in function <...uild/neovim/neovim/test/functional/core/startup_spec.lua:118>

More:

profiling:/home/travis/build/neovim/neovim/build/src/nvim/CMakeFiles/nvim.dir/ops.c.gcda:Merge mismatch for function 37

From https://travis-ci.org/neovim/neovim/jobs/560116343:

[----------] Running tests from /home/travis/build/neovim/neovim/test/functional/core/channels_spec.lua
[ RUN      ] channels can connect to socket: 0.03 ms SKIP
[ RUN      ] channels can use stdio channel: FAIL
test/functional/helpers.lua:113: Expected objects to be the same.
Passed in:
(table: 0x4081bd08) {
  [1] = 'notification'
  [2] = 'stderr'
 *[3] = {
    [1] = 3
   *[2] = {
     *[1] = 'profiling:/home/travis/build/neovim/neovim/build/src/nvim/CMakeFiles/nvim.dir/ops.c.gcda:Merge mismatch for function 37'
      [2] = '' } } }
Expected:
(table: 0x4b537ae8) {
  [1] = 'notification'
  [2] = 'stderr'
 *[3] = {
    [1] = 3
   *[2] = {
     *[1] = '' } } }
stack traceback:
	test/functional/helpers.lua:113: in function 'expect_twostreams'
	...ild/neovim/neovim/test/functional/core/channels_spec.lua:93: in function <...ild/neovim/neovim/test/functional/core/channels_spec.lua:61>
[ RUN      ] channels can use stdio channel with pty: FAIL
...ild/neovim/neovim/test/functional/core/channels_spec.lua:106: Expected objects to be the same.
Passed in:
(table: 0x41a2d838) {
  [1] = 'notification'
  [2] = 'stdout'
 *[3] = {
    [1] = 3
   *[2] = {
'
      [2] = '' } } }
Expected:
(table: 0x40bd56e0) {
  [1] = 'notification'
  [2] = 'stdout'
 *[3] = {
    [1] = 3
   *[2] = {
     *[1] = '[1, ['TEXT', ''], 'stdin']' } } }
stack traceback:
	...ild/neovim/neovim/test/functional/core/channels_spec.lua:106: in function 'expect_twoline'
	...ild/neovim/neovim/test/functional/core/channels_spec.lua:132: in function <...ild/neovim/neovim/test/functional/core/channels_spec.lua:110>

[blueyed]

For reference: #10480 was merged now, using gcc9 for the coverage job on Linux. Hopefully this fixes problems in this regard, but should at least provide GCOV_ERROR_FILE now.

[justinmk]

related: #13312

Let's see how it goes if/when we restore the gcov build job.