Provide a fallback for M_PI and M_PI_2 (#412)

As C standards does not define M_PI_2 provide a fallback and
factor out common definitions to math_utils.h

src/Makefile.am

@@ -58,7 +58,7 @@ noinst_HEADERS = \
 	keyer.h keystroke_names.h \
 	lancode.h last10.h listmessages.h log_utils.h \
 	log_to_disk.h logit.h logview.h \
-	makelogline.h messagechange.h muf.h \
+	makelogline.h math_utils.h messagechange.h muf.h \
 	nicebox.h note.h netkeyer.h\
 	paccdx.h parse_logcfg.h printcall.h \
 	paccdx.h parse_logcfg.h plugin.h printcall.h \

src/math_utils.h

@@ -0,0 +1,37 @@
+/*
+ * Tlf - contest logging program for amateur radio operators
+ * Copyright (C) 2023	Thomas Beierlein <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+
+#ifndef MATH_UTILS_H
+#define MATH_UTILS_H
+
+/* Make sure math.h is included before the following definitions */
+#ifndef MATH_H
+#include <math.h>
+#endif
+
+/* provide a fallback for M_PI_2 as C standard does not guarantee the definition
+of these constant */
+#ifndef M_PI_2
+# define M_PI_2         1.57079632679489661923  /* pi/2 */
+#endif
+
+#define RADIAN  (90.0 / M_PI_2)
+
+#endif

src/muf.c

@@ -27,12 +27,12 @@
 #include "get_time.h"
 #include "globalvars.h"
 #include "getwwv.h"
+#include "math_utils.h"
 #include "sunup.h"
 #include "qrb.h"
 #include "tlf_panel.h"
 #include "ui_utils.h"
 
-
 // message splitters:
 // line[0] - original line, content can be modified in-place
 // line[1],line[2] - pointers to subsequent lines within line[0], initially NULL
@@ -183,7 +183,6 @@ September 26, 1986.
 *********************************************************************/
 
 #define ARC_IN_KM 111.2         // same as in Hamlib's locator.c
-#define RADIAN  (180.0 / M_PI)
 
 int month;
 

src/sunup.c

@@ -22,9 +22,7 @@
 #include <time.h>
 
 #include "get_time.h"
-
-#define RADIAN  (180.0 / M_PI)
-
+#include "math_utils.h"
 
 /** Compute sun up and down at given latitude
  *