examples: move MSVC compatibility macros into common header

We currently have two locations in our examples where we define
the same compatibility wrappers for MSVC. Move them into
"common.h" to avoid duplication and make them available to other
examples.

examples/blame.c

@@ -14,11 +14,6 @@
 
 #include "common.h"
 
-#ifdef _MSC_VER
-#define snprintf sprintf_s
-#define strcasecmp strcmpi
-#endif
-
 /**
  * This example demonstrates how to invoke the libgit2 blame API to roughly
  * simulate the output of `git blame` and a few of its command line arguments.

examples/common.h

@@ -26,6 +26,11 @@
 #endif
 #endif
 
+#ifdef _MSC_VER
+#define snprintf sprintf_s
+#define strcasecmp strcmpi
+#endif
+
 #define ARRAY_SIZE(x) (sizeof(x)/sizeof(*x))
 #define UNUSED(x) (void)(x)
 

examples/merge.c

@@ -15,10 +15,6 @@
 #include "common.h"
 #include <assert.h>
 
-#ifdef _MSC_VER
-#define snprintf sprintf_s
-#endif
-
 /** The following example demonstrates how to do merges with libgit2.
  *
  * It will merge whatever commit-ish you pass in into the current branch.