MDEV-38499: cmake and compile errors on MacOSX when compiling mariadb from a git tree

[gkodinov]

Fix the warnings issued by a normal MacOSX compile.

Problems:

1. sprintf is deprecated in favor of snprintf
2. bison incorrectly issues a warning when it sees "b4_bin"
3. MacOSX linker issues a warning about duplicate mysys/dbug/etc libraries.

On 1: replaced the relevant sprintf with snprintf. On 2: worked around by adding a compiler define with a different name
aliasing the character set variable used with a name that
won't trigger the bison warning
On 3: This is due to the fact that there's a circular dependecy between
mysys and dbug (among others). Turned the warning off by adding a macro
to suppress the duplicate library warning.
Applied the macro to all targets that have a dependency on
the mysys/dbug/strings libraries

[dr-m]

Is there a particular reason why we are not working around the Bison bug in the earliest maintained branch (10.6)?

[dr-m]

I am sad to see that my experimental change 615340f in #3616 to violite.h has not been included. As I noted back then, it only suppressed a number of deprecation warnings for the use of the unsafe and obsolete sprintf function, which had been superceded by snprintf in ISO/IEC 9899:1999 (C99). Some use of that function still remains here. I’d like to see a follow-up ticket to be filed to address this.

[vaintroub]

Some formatting and comment nitpicks

[vaintroub]

looks good to me