[PATCH v3 0/4] Ensure that we can build without libgen.h

This mini series adds a fall-back for the `dirname()` function that we use e.g. in git-am. This is necessary because not all platforms have a working libgen.h.

While at it, we ensure that our basename() drop-in conforms to the POSIX specifications.

In addition to the interdiff vs v2, the commit message was fixed to mention basename("") as cornercase (not basename("abc")).

Johannes Schindelin (4):
  Refactor skipping DOS drive prefixes
  compat/basename: make basename() conform to POSIX
  Provide a dirname() function when NO_LIBGEN_H=YesPlease
  t0060: verify that basename() and dirname() work as expected

 compat/basename.c     |  66 ++++++++++++++++++--
 compat/mingw.c        |  14 ++---
 compat/mingw.h        |  10 ++-
 git-compat-util.h     |  10 +++
 path.c                |  14 ++---
 t/t0060-path-utils.sh |   3 +
 test-path-utils.c     | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 259 insertions(+), 24 deletions(-)

Interdiff vs v2:

 diff --git a/test-path-utils.c b/test-path-utils.c
 index 74e74c9..4ab68ac 100644
 --- a/test-path-utils.c
 +++ b/test-path-utils.c
 @@ -40,15 +40,15 @@ static void normalize_argv_string(const char **var, const char *input)
  }
  
  struct test_data {
 -	char *from;  /* input:  transform from this ... */
 -	char *to;    /* output: ... to this.            */
 +	const char *from;  /* input:  transform from this ... */
 +	const char *to;    /* output: ... to this.            */
  };
  
  static int test_function(struct test_data *data, char *(*func)(char *input),
  	const char *funcname)
  {
  	int failed = 0, i;
 -	static char buffer[1024];
 +	char buffer[1024];
  	char *to;
  
  	for (i = 0; data[i].to; i++) {
 @@ -61,10 +61,10 @@ static int test_function(struct test_data *data, char *(*func)(char *input),
  		if (strcmp(to, data[i].to)) {
  			error("FAIL: %s(%s) => '%s' != '%s'\n",
  				funcname, data[i].from, to, data[i].to);
 -			failed++;
 +			failed = 1;
  		}
  	}
 -	return !!failed;
 +	return failed;
  }
  
  static struct test_data basename_data[] = {
 @@ -132,7 +132,6 @@ static struct test_data basename_data[] = {
  
  #endif
  #endif
 -	{ NULL,              "."    },
  	{ NULL,              NULL   }
  };
  
 @@ -197,7 +196,6 @@ static struct test_data dirname_data[] = {
  
  #endif
  #endif
 -	{ NULL,              "."      },
  	{ NULL,              NULL     }
  };