MDEV-27686 Moving libexecinfo out of FreeBSD / OpenBSD specific CMake…

… code

On all Unix platforms, link libexecinfo as system library,
if it contains backtrace_symbols_fd function, and libc does not contain
this function

Also remove cmake/os/OpenBSD.cmake, as after the fix it serves no purpose.

cmake/os/FreeBSD.cmake

@@ -28,8 +28,3 @@ SET(EXECINFO_ROOT /usr/local CACHE INTERNAL "Where to find execinfo library and
 INCLUDE_DIRECTORIES(${EXECINFO_ROOT}/include)
 SET(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${EXECINFO_ROOT}/include)
 SET(ENV{LIB} "$ENV{LIB}:${EXECINFO_ROOT}/lib")
-FIND_LIBRARY(EXECINFO NAMES execinfo)
-IF(EXECINFO)
- SET(LIBEXECINFO ${EXECINFO})
-ENDIF()
-

configure.cmake

@@ -134,6 +134,8 @@ IF(UNIX)
   IF(NOT LIBRT)
     MY_SEARCH_LIBS(clock_gettime rt LIBRT)
   ENDIF()
+  MY_SEARCH_LIBS(backtrace_symbols_fd execinfo LIBEXECINFO)
+
   set(THREADS_PREFER_PTHREAD_FLAG ON)
   FIND_PACKAGE(Threads)