Compilation issues with C99

[adamjstewart]

I'm trying to compile fstrack on macOS 10.15.7 with Apple Clang 12.0.0. I'm getting the following compilation issue:

cornerflow.c:29:3: error: implicit declaration of function 'sincos' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
  sincos(alpha,&sina,&cosa);
  ^
cornerflow.c:29:3: note: did you mean '__sincos'?
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/math.h:655:29: note: '__sincos' declared here
__header_always_inline void __sincos(double __x, double *__sinp, double *__cosp) {
                            ^
cornerflow.c:91:3: error: implicit declaration of function 'sincos' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
  sincos(theta,&sint,&cost);
  ^
cornerflow.c:104:3: error: implicit declaration of function 'sincos' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
  sincos(theta,&sint,&cost);
  ^
cornerflow.c:114:3: error: implicit declaration of function 'sincos' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
  sincos(theta,&sint,&cost);
  ^
cornerflow.c:132:3: error: implicit declaration of function 'sincos' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
  sincos(theta,&sint,&cost);
  ^
5 errors generated.
make: *** [objects/x86_64//cornerflow.o] Error 1