BUILD_TYPE=mysql_release to remove compile flags

In cmake/build_configurations/mysql_release.cmake, triggered by BUILD_TYPE=mysql_release there a bunch of compiler flags set. There are maintained only when something breaks.

Currently the CMAKE_BUILD_TYPE=RelWithDeb info is extensively tested on what its default compile/warning flags are.

The BUILD_TYPE=mysql_release adds a bunch of O3 C/CXX_FLAGS along with -fno-strict-aliasing (MDEV-20277) and others.

The BUILD_TYPE=mysql_release is tested with the following BB builders:

• rpm-autobake / deb-autobake (by virtue of debian/control)
• bintar
• x86-debian-12-fulltest / amd64-ubuntu-2204-fulltest (f_fulltest)
• windows_msi (not relevant, cflags only changed under UNIX)

We don't have enough build resources to do CMAKE_BUILD_TYPE=RelWithDeb info and a CMAKE_BUILD_TYPE=mysql_release..

As extensive tests are not run on autobake or bintars there is only two builders or specific architectures and compiler versions than actually perform reasonable testing for BUILD_TYPE=mysql_release. So the rest of our releases are getting released on under tested code.

Issues like MDEV-39148 discover hidden differences in BUILD_TYPE=mysql_release.

As such, lets remove all the "# Compiler options
IF(UNIX)" onwards in the cmake/build_configurations/mysql_release.cmake and if there's a benefit and stability to O3, lets put it near the other compile/warning customisation in cmake/maintainer.cmake.

For reference the default cmake cflags under Linux:

CMakeCache.txt:// CMAKE_C_FLAGS used) Debug Release RelWithDebInfo MinSizeRel

CMakeCache.txt:CMAKE_C_FLAGS:STRING=

CMakeCache.txt:CMAKE_C_FLAGS_DEBUG:STRING=-g

CMakeCache.txt:CMAKE_C_FLAGS_MINSIZEREL:STRING=-Os -DNDEBUG

CMakeCache.txt:CMAKE_C_FLAGS_RELEASE:STRING=-O3 -DNDEBUG

CMakeCache.txt:CMAKE_C_FLAGS_RELWITHDEBINFO:STRING=-O2 -g -DNDEBUG