Declare (or replace) C++11 functions

[jameshiebert]

From Professor Brian D. Ripley:

[climdex.pcic] use[s] functions/macros which are not part of C++98: see the logs
at http://www.stats.ox.ac.uk/pub/bdr/C++Solaris .

Functions

 erf expm1 floorf fmin fminf fmax lgamma lround loglp round snprintf
 strcasecmp trunc

were introduced in C99 and so are part of C++11 but not C++98 and the
Solaris C++ compiler does not provide prototypes for them: unfortunately
g++ does not warn of this. (R is currently including from R.h legacy
headers such as math.h to work around this, but that will be changed
for R 3.4.0.)

R's Rmath.h provides fmax2 fmin2 fround ftrunc gammafn : please use
them as appropriate. Also, erf can be replaced by a call to R's pnorm (the
translation is in the R help file for pnorm).

C++98's floor has a method for floats, so floorf is not needed in C++ .

Constants M_LN2 (gmp), M_SQRT2 (mixAK) and M_PI4 (simLife) are not
C++98. You can get them by including Rmath.h (or copy them from there).

For wtcrsk, isnan is not C++98, but R provides ISNAN for use in C++.

For SSN, strdup is a GNU/POSIX extension to C and not in any C++
standard hence not declared in according to the standard.
Substitutes are widely available: we suggest you use one.

For the rest, the best solution would seem to be to declare that C++11
is used: see 'Writing R Extensions'.