On Windows 7 x64.
Gcc: 4.8.2 x86_64-w64-mingw32
hg cd4772ba9573 (release-branch.go1.4)

Installed from http://win-builds.org/

System still builds and runs fine. Appears to have appeared after I installed a new
version of gcc (upgraded when I needed the newer version for a different project).

--- FAIL: TestStdcallAndCDeclCallbacks (0.22s)
        syscall_windows_test.go:373: failed to build dll: exit status 1 - test.c: In function 'cdecl2':
                test.c:5:12: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
                  for(i=0;i<(int)n;i++){
                            ^
                test.c:6:3: warning: passing argument 1 of 'f' makes pointer from integer without a cast [enabled by default]
                   f(1,2);
                   ^
                test.c:6:3: note: expected 'void *' but argument is of type 'int'
                test.c:6:3: warning: passing argument 2 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:6:3: note: expected 'void *' but argument is of type 'int'
                test.c: In function 'stdcall2':
...
                test.c:118:3: warning: passing argument 1 of 'f' makes pointer from integer without a cast [enabled by default]
                   f(1,2,3,4,5,6,7,8,9);
                   ^
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 2 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 3 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 4 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 5 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 6 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 7 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 8 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c:118:3: warning: passing argument 9 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:118:3: note: expected 'void *' but argument is of type 'int'
                test.c: In function 'stdcall9':
                test.c:125:12: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
                  for(i=0;i<(int)n;i++){
                            ^
                test.c:126:3: warning: passing argument 1 of 'f' makes pointer from integer without a cast [enabled by default]
                   f(1,2,3,4,5,6,7,8,9);
                   ^
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 2 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 3 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 4 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 5 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 6 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 7 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 8 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'
                test.c:126:3: warning: passing argument 9 of 'f' makes pointer from integer without a cast [enabled by default]
                test.c:126:3: note: expected 'void *' but argument is of type 'int'�
                c:/dev/winbuilds/bin/../lib64/gcc/x86_64-w64-mingw32/4.8.2/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lgcc_s
                c:/dev/winbuilds/bin/../lib64/gcc/x86_64-w64-mingw32/4.8.2/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lgcc_s
                collect2.exe: error: ld returned 1 exit status