Git Resolver: Fix detection of LibGit2
Before this update detecting LibGit2 would fail, if we treated warnings
as errors (`-Werror`). The cause of this problem was that compiling
`gitresolver_test.c` produced a warning about an incorrect return value.
#include <git2.h>
-void main (void)
+int main (void)
{
git_libgit2_init ();
git_index_add_frombuffer (NULL, NULL, NULL, (size_t) NULL);
git_libgit2_shutdown ();
+ return 0;
}
