inconsistent fileslashes in `#line` directives

[firewave]

#line 1 "E:/a.h"
void f ( ) ;
#line 1 "E:/b.h"
void f ( ) ;
#line 4 "E:\a.cpp"
int i ;

The given file was E:\a.cpp.

[firewave]

#line 1 "../simplecpp/a.h"
int g ;
#line 3 "../simplecpp//a.cpp"
int i ;

The input was ../simplecpp//a.cpp.