MDEV-39086 MSAN/UBSAN/ASAN builds run without basic optimization (fix)

[grooverdan]

As noted the MSVC supports a different range of optimization flags and therefore not setting -Og.

When CMAKE_BUILD_TYPE is specified its in a mixed case, but the CMAKE_C{,XX}FLAGS${BUILD_TYPE} is always upper case.

[vaintroub]

I have thought about it a bit, and I think the best way to express what you like to express is

IF(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Clang|AppleClang)"
  AND (WITH_ASAN OR WITH_UBSAN OR WITH_MSAN))
  SET(_all_lang_flags " ${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_DEBUG} ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_DEBUG}")
  IF(NOT _all_lang_flags MATCHES " -O[0-9sgzf]")
    ADD_COMPILE_OPTIONS($<$<CONFIG:Debug>:-Og>)
  ENDIF()
ENDIF()

Explanation

• restrict to compilers you know and care about (MSVC btw also has -Og but those are very aggressive optimizations)
• only add this -Og to Debug configuration, and only if no optimization flags are set
• Do it is a way that works with multi-config generators such as Xcode or Ninja Multiconfig (I exclude VS here, since it is irrelevant for the change, but others are not irrelevant)
• "modern" (i.e not older that 3.0 CMake) add_compiler_options. No need to check and set . You know the compilers you care about.

Your change, as-is, would not work with multi-config, in fact it would -Og with all configurations of multi-config generator

[grooverdan]

Thanks @vaintroub , updated with your recommendation and tested it. It looks very good. Feel free to merge or request improved descriptions.