Updates the cmake build system

It's still has some work, but it successfully builds on
all 3 main platforms.  Some of the outstanding items
include:

   Install target testing (mostly important for Linux)
   CMakeList clean up and comments
   Debug and Release build verification
   Audit of compile/link options
   Need a Mac signed and notarized build
   (and probably more)

cmake-proxies/libsndfile/clipcheck.c

@@ -0,0 +1,44 @@
+#define  _ISOC9X_SOURCE 1
+#define _ISOC99_SOURCE  1
+#define  __USE_ISOC99   1
+#define __USE_ISOC9X 1
+#include <math.h>
+#include <stdio.h>
+int main (void)
+{
+   double fval ;
+   int k, ival ;
+   int pos = 0 ;
+   int neg = 0 ;
+
+   fval = 1.0 * 0x7FFFFFFF ;
+   for (k = 0 ; k < 100 ; k++)
+   {
+      ival = (lrint (fval)) >> 24 ;
+      if (ival != 127)
+      {
+         pos = 1 ;
+         break ;
+      }
+
+      fval *= 1.2499999 ;
+   }
+
+   fval = -8.0 * 0x10000000 ;
+   for (k = 0 ; k < 100 ; k++)
+   {
+      ival = (lrint (fval)) >> 24 ;
+      if (ival != -128)
+      {
+         neg = 1 ;
+         break ;
+      }
+
+      fval *= 1.2499999 ;
+   }
+
+   printf("%d;%d", pos, neg) ;
+
+   return 0 ;
+}
+