lib: Move the bupsplit selftest into our test framework

We weren't running it before. Also I switched it to use GLib. Preparation for
some oxidation work (having an implementation of bupsplit in Rust).

I exported another function to do the raw rollsum operation which is what this
test suite uses.

Closes: #655
Approved by: jlebon

src/libostree/bupsplit.h

@@ -30,6 +30,9 @@
 #ifndef __BUPSPLIT_H
 #define __BUPSPLIT_H
 
+#include <stdint.h>
+#include <sys/types.h>
+
 #define BUP_BLOBBITS (13)
 #define BUP_BLOBSIZE (1<<BUP_BLOBBITS)
 #define BUP_WINDOWBITS (7)
@@ -38,9 +41,9 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-    
+
+uint32_t bupsplit_sum(uint8_t *buf, size_t ofs, size_t len);
 int bupsplit_find_ofs(const unsigned char *buf, int len, int *bits);
-int bupsplit_selftest(void);
 
 #ifdef __cplusplus
 }