- MSVC deprecated the standard POSIX names for Bessel functions in
favour of underscore prefixed versions.
- Previously we were checking for the presence of the newer underscore
functions via a macro, which fails as the functions are not defined
as macros.
- Now we check via a check_cxx_source_compiles() if the newer underscore
prefixed versions exist when compiling on MSVC and use a new Ceres
configuration #define to switch on their presence in jet.h
Change-Id: I430880bde2981d12f4d03dbc94d903b9842e887e
Alex Stewart