refactor: the long goodbye

long is 32 bits on windows, while it is 64 bits on other architectures.
This makes the type suboptimal for a codebase meant to be
cross-platform. Replace it with more appropriate integer types.

src/xdiff/xdiff.h

@@ -69,12 +69,12 @@ extern "C" {
 
 typedef struct s_mmfile {
 	char *ptr;
-	long size;
+	int size;
 } mmfile_t;
 
 typedef struct s_mmbuffer {
 	char *ptr;
-	long size;
+	int size;
 } mmbuffer_t;
 
 typedef struct s_xpparam {