Add headers and docs for the acosh functions.

ORCACDefs/math.h

@@ -69,6 +69,9 @@ int __fpcompare(long double, long double, short);
 double          acos(double);
 float           acosf(float);
 long double     acosl(long double);
+double          acosh(double);
+float           acoshf(float);
+long double     acoshl(long double);
 double          asin(double);
 float           asinf(float);
 long double     asinl(long double);

ORCACDefs/tgmath.h

@@ -36,6 +36,7 @@
 #define __tg_x_y(fn,x,y) __tg_real_x_y(fn,(x),(y))
 
 #define acos(x)         __tg_x(acos,(x))
+#define acosh(x)        __tg_x(acosh,(x))
 #define asin(x)         __tg_x(asin,(x))
 #define atan(x)         __tg_x(atan,(x))
 #define atan2(y,x)      __tg_real_x_y(atan2,(y),(x))

cc.notes

@@ -896,6 +896,13 @@ These macros accept arguments of any real floating types, i.e. float, double, or
 
 Also, note that under ORCA/C these functions generally will not set errno for error conditions (e.g. domain and range errors).  However, they do set floating-point exceptions as appropriate.  The <fenv.h> functions documented above can be used to retrieve these exceptions, allowing errors to be detected.
 
+#include <math.h>
+dou         acosh(double x);
+float       acoshf(float x);
+long double acoshl(long double x);
+
+These functions return the (non-negative) inverse hyperbolic cosine of x.
+
 #include <math.h>
 double      cbrt(double x);
 float       cbrtf(float x);