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/famcheck.c

@@ -0,0 +1,12 @@
+#include <stdlib.h>
+typedef struct
+{
+   int k;
+   char buffer [];
+} MY_STRUCT;
+int main(void)
+{
+   MY_STRUCT *p = calloc (1, sizeof (MY_STRUCT) + 42);
+   return 0;
+}
+