Added define for MSVC

needed for compatibility with [MSVC](https://docs.microsoft.com/en-us/cpp/c-runtime-library/math-constants?redirectedfrom=MSDN&view=msvc-160)

src/functions/acalc.h

@@ -2,6 +2,7 @@
 #define ACALC_H
 
 #include <QDateTime>
+#define _USE_MATH_DEFINES // needed for MSVC
 #include <cmath>
 #include <QDebug>
 /*!