ImportC: Overriding standard search paths for C includes

[kdevel]

Given the C source `cmysql.c` containing just

```C
#include <mysql/mysql.h>
```

Assume on a Linux system there is not only

```
/usr/include/mysql/mysql.h        (1)
```

but also

```
/tmp/dummyinclude/mysql/mysql.h   (2)
```

In order to instruct gcc to include the second file I compile with

```
gcc -I /tmp/dummyinclude cmysql.c
```

Now I have a D file test.d containing only

```D
import cmysql;
```

How do I get ImportC to include (2)? On my machine

```
dmd -I(=)/tmp/dummyinclude test.d
```

always `lstat`s and `open`s `/usr/include/mysql/mysql.h`?