cmake: Add C99 requirement to target properties
cmake: Add C99 requirement to target properties

stdint.h and uintmax_t require a C99 capable compiler. Let CMake know.

Fixes: 0e70150002ab ("cmocka: Replace LargestIntegralType with uintmax_t")
Signed-off-by: Alexander Dahl <e4ea294c062c525643df036a35ca579b905fa400@thorsis.com>
Reviewed-by: Andreas Schneider <5be00ddc76278cf6077f5047ca3384a88460c671@cryptomilk.org>
clibs/cmocka,clibs/cmocka