[patch] simplify code in os_cygwin.cpp

[Enrico Forestieri]

Recent versions of the cygwin dll have an internal function for
syncing the Windows environment. The attached patch uses this
function, leading to much simplified code.

JMarc, Ok to also apply it to branch?

-- 
Enrico

Index: src/support/os_cygwin.cpp
===================================================================
--- src/support/os_cygwin.cpp   (revision 19330)
+++ src/support/os_cygwin.cpp   (working copy)
@@ -145,45 +145,23 @@ string convert_path_list(string const & 
 
 void os::init(int, char *[])
 {
-       // Copy cygwin environment variables to the Windows environment
-       // if they're not already there.
+       // Make sure that the TEMP variable is set
+       // and sync the Windows environment.
 
        char **envp = environ;
-       char curval[2];
        string var;
-       string val;
        bool temp_seen = false;
 
-       while (envp && *envp) {
-               val = split(*envp++, var, '=');
-
+       while (envp && *envp && !temp_seen) {
+               split(*envp++, var, '=');
                if (var == "TEMP")
                        temp_seen = true;
-
-               if (GetEnvironmentVariable(var.c_str(), curval, 2) == 0
-                               && GetLastError() == ERROR_ENVVAR_NOT_FOUND) {
-                       /* Convert to Windows style where necessary */
-                       if (var == "PATH" || var == "LD_LIBRARY_PATH") {
-                               string const winpathlist =
-                                   convert_path_list(val, PathStyle(windows));
-                               if (!winpathlist.empty()) {
-                                       SetEnvironmentVariable(var.c_str(),
-                                               winpathlist.c_str());
-                               }
-                       } else if (var == "HOME" || var == "TMPDIR" ||
-                                       var == "TMP" || var == "TEMP") {
-                               string const winpath =
-                                       convert_path(val, PathStyle(windows));
-                               SetEnvironmentVariable(var.c_str(), 
winpath.c_str());
-                       } else {
-                               SetEnvironmentVariable(var.c_str(), 
val.c_str());
-                       }
-               }
        }
        if (!temp_seen) {
                string const winpath = convert_path("/tmp", PathStyle(windows));
-               SetEnvironmentVariable("TEMP", winpath.c_str());
+               ::setenv("TEMP", winpath.c_str(), true);
        }
+       cygwin_internal(CW_SYNC_WINENV);
 }