build failure on MacOS

Building MariaDB server of any version starting from 10.1 fails on MacOS.
Building failure happens on attempt to link any executable file.
Building process breaks due to the use of the unsupported -z flag in the linker options.
In result cmake terminates building with the following output:
ld: unknown option: -z
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Unsupported linker option is added by the following cmake macros

  MY_CHECK_AND_SET_LINKER_FLAG("-Wl,-z,relro,-z,now")

that was introduced by the commit

commit 7473e1841c630d86f1873a2a7afacb53955b3f6f (HEAD)

Author: Daniel Black <daniel@linux.ibm.com>

Date:   Tue May 5 11:57:20 2020 +1000

check_linker_flag: use for linker flags

-Wl,-z,relro,-z,now are linker flags and should

be checked as such.