build: Remove unnecessary AC_CHECK_FUNCS calls. * configure.ac: Remove unnecessary AC_CHECK_FUNCS calls. Segregate some AC_CHECK_FUNCS calls to only be tested when building GUI. Segregate some AC_CHECK_FUNCS calls to only be tested on certain platforms. * __magick_read__.cc: Shorten comment to less than 80 characters. * ov-ch-mat.cc: Add workaround for toascii if function is not available. * lo-mappers.cc: Use log2f and exp2f if they are available. Otherwise, fall back to double versions log2 and exp2 or other workaround.

--- a/liboctave/numeric/lo-mappers.cc
+++ b/liboctave/numeric/lo-mappers.cc
@@ -317,7 +317,9 @@
 float
 xlog2 (float x)
 {
-#if defined (HAVE_LOG2)
+#if defined (HAVE_LOG2F)
+  return log2f (x);
+#elif defined (HAVE_LOG2)
   return log2 (x);
 #else
 #if defined (M_LN2)
@@ -345,7 +347,9 @@
 float
 xexp2 (float x)
 {
-#if defined (HAVE_EXP2)
+#if defined (HAVE_EXP2F)
+  return exp2f (x);
+#elif defined (HAVE_EXP2)
   return exp2 (x);
 #else
 #if defined (M_LN2)