Added specific test for Compilation Database to reproduce issue #4275…

[TZe-0xff]

Added specific test for Compilation Database to reproduce issue SCons#4275 with TempFileMunge

This new test allows to reproduce issue SCons#4275 in a platform independent way.
The only drawback is that I needed to disable actual build of output since I didn't find a way to execute command line from file using python.

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt (and read the README.rst)
• I have updated the appropriate documentation

[TZe-0xff]

By the way, runtest outputs with your fix reverted :

zeisslt@OBELZEISSLT MINGW64 /c/Data/Workspaces/Python/Scons/scons (fix_4275_comp_db_with_TEMPFILE_test|REVERTING)
$ python runtest.py test/CompilationDatabase/*
1/3 (33.33%) C:\Python37-32\python.exe test/CompilationDatabase/basic.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
PASSED
2/3 (66.67%) C:\Python37-32\python.exe test/CompilationDatabase/tmpfile.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
FAILED test of C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py
        at line 522 of C:\Data\Workspaces\Python\Scons\scons\testing\framework\TestCommon.py (must_match)
        from line 75 of test/CompilationDatabase/tmpfile.py
Unexpected contents of `compile_commands_only_arg.json'
contents =======================================================================
3c3
<         "command": "C:\\Python37-32\\python.exe mygcc.py cc -o test_main.o -c test_main.c",
---
>         "command": "C:\\Python37-32\\python.exe @C:\\Users\\zeisslt\\AppData\\Local\\Temp\\tmphyugqbx1.lnk",
3/3 (100.00%) C:\Python37-32\python.exe test/CompilationDatabase/variant_dir.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
PASSED

Failed the following test:
        test/CompilationDatabase/tmpfile.py

And then with your fix :

zeisslt@OBELZEISSLT MINGW64 /c/Data/Workspaces/Python/Scons/scons (fix_4275_comp_db_with_TEMPFILE_test)
$ python runtest.py test/CompilationDatabase/*
1/3 (33.33%) C:\Python37-32\python.exe test/CompilationDatabase/basic.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
PASSED
2/3 (66.67%) C:\Python37-32\python.exe test/CompilationDatabase/tmpfile.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
PASSED
3/3 (100.00%) C:\Python37-32\python.exe test/CompilationDatabase/variant_dir.py
C:\Python37-32\python.exe "C:\Data\Workspaces\Python\Scons\scons\scripts\scons.py"
PASSED

[bdbaddog]

Merging. I'll likely make a few tweaks once I merge into my branch.