Simplify cmake/compilerFlags.cmake to avoid problem with exotic environments

[piponazo]

Is your feature request related to a problem? Please describe.
In cmake/compilerFlags.cmake we have a section were we try to find out if some of the following compiler flags are available and we try to use them: -fstack-clash-protection -fcf-protection -fstack-protector-strong -Wp,-D_GLIBCXX_ASSERTIONS -Wp,-D_FORTIFY_SOURCE=2.

When this was introduced it looked like a good idea, and it has helped us to find/debug some bugs. However, it is also true that we had to deal with those flags to enable the support of non common Linux Distributions or other more existing development environments (CYGWIN, MSYS2-MinGW, etc).

Describe the solution you'd like
I think it would be beneficial to remove the complex logic in cmake/compilerFlags.cmake around those compiler flags, to have better support for exotic environments and linux distributions. Linux distribution packagers can still pass those compiler flags when building the Exiv2 library, by means of the CMAKE_CXX_FLAGS variable when calling cmake for the first time.

[clanmills]

I think that is more-or-less the same as #1235 and #1406.

[piponazo]

I think I created this issue when I was working in the old-master branch and I was having troubles with some of the less usual environments (trying to add support for ARM or MinGW; I cannot recall with precision at the moment).

I'll double check these things when I start working on main.