win32: interpret absolute paths as relative to %SYSTEMDRIVE%

BusyBox contains hardcoded references to absolute paths which
are unique in the *nix world but on Microsoft Windows are
interpreted as being on the current drive.  To make these unique
again consider them to be relative to %SYSTEMDRIVE%.

Support this by adding functions to:

- determine the system drive (not using the environment variable);
- change a process's current directory to the root of the system drive;
- make relative paths absolute before changing directory (if needed).

The following applications have been modified:

- ash references /etc/profile from the system drive;
- dpkg places its data store on and installs files to the system drive;
- rpm installs files to the system drive;
- man looks for configuration files and man pages on the system drive.

See GitHub issue #158.

1 files changed, 3 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 7c9423cad..d77a9beb9 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -525,3 +525,6 @@ void hide_console(void);
 
 int unc_root_len(const char *dir);
 int root_len(const char *path);
+char *get_system_drive(void);
+int chdir_system_drive(void);
+char *xabsolute_path(char *path);