Add support for %PROGRAMDATA%\Git\config

Documentation/config.txt

@@ -6,7 +6,9 @@ the Git commands' behavior. The `.git/config` file in each repository
 is used to store the configuration for that repository, and
 `$HOME/.gitconfig` is used to store a per-user configuration as
 fallback values for the `.git/config` file. The file `/etc/gitconfig`
-can be used to store a system-wide default configuration.
+can be used to store a system-wide default configuration. On Windows,
+configuration can also be stored in `C:\ProgramData\Git\config`; This
+file will be used also by libgit2-based software.
 
 The configuration variables are used by both the Git plumbing
 and the porcelains. The variables are divided into sections, wherein

compat/mingw.c

@@ -2378,3 +2378,12 @@ void mingw_startup()
 	/* init length of current directory for handle_long_path */
 	current_directory_len = GetCurrentDirectoryW(0, NULL);
 }
+
+const char *windows_wide_config(void)
+{
+	static struct strbuf windows_wide = STRBUF_INIT;
+	if (!windows_wide.len)
+		strbuf_addf(&windows_wide,
+			"%s\\Git\\config", getenv("PROGRAMDATA"));
+	return windows_wide.buf;
+}

compat/mingw.h

@@ -392,6 +392,8 @@ static inline char *mingw_find_last_dir_sep(const char *path)
 int mingw_offset_1st_component(const char *path);
 #define offset_1st_component mingw_offset_1st_component
 #define PATH_SEP ';'
+extern const char *windows_wide_config(void);
+#define git_super_config windows_wide_config
 #ifndef __MINGW64_VERSION_MAJOR
 #define PRIuMAX "I64u"
 #define PRId64 "I64d"

config.c

@@ -1204,11 +1204,18 @@ int git_config_system(void)
 int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 {
 	int ret = 0, found = 0;
+	const char *super_config = git_super_config();
 	char *xdg_config = NULL;
 	char *user_config = NULL;
 
 	home_config_paths(&user_config, &xdg_config, "config");
 
+	if (super_config && git_config_system() &&
+			!access(super_config, R_OK)) {
+		ret += git_config_from_file(fn, super_config, data);
+		found += 1;
+	}
+
 	if (git_config_system() && !access_or_die(git_etc_gitconfig(), R_OK, 0)) {
 		ret += git_config_from_file(fn, git_etc_gitconfig(),
 					    data);

git-compat-util.h

@@ -307,6 +307,10 @@ static inline char *git_find_last_dir_sep(const char *path)
 #define find_last_dir_sep git_find_last_dir_sep
 #endif
 
+#ifndef git_super_gitconfig
+#define git_super_gitconfig NULL
+#endif
+
 #if defined(__HP_cc) && (__HP_cc >= 61000)
 #define NORETURN __attribute__((noreturn))
 #define NORETURN_PTR