* Preserve existing release flags in MSVC
Without this the `/MD` flag is lost on Release builds,
resulting in the below error when using a Ninja CMake generator with
VS2019 compiler. Before replacement `/MD /O2 /Ob2 /DNDEBUG`, after replace
`/MD /Od /Ob0 /DNDEBUG`
```
harness.lib(testHarness.cpp.obj) : error LNK2038: mismatch detected for 'RuntimeLibrary': value 'MD_DynamicRelease' doesn't match value 'MT_StaticRelease' in test_conversions.cpp.obj
```
* Remove Visual Studio 2005 release flag workarounds
The maintenance of the conformance tests is moving to Github.
This commit contains all the changes that have been done in
Gitlab since the first public release of the conformance tests.
Signed-off-by: Kevin Petit kevin.petit@arm.com