Fix DLL export forwarding

I noticed it when I was trying to set a breakpoint at ExitProcess:
```
(gdb) b ExitProcess
Breakpoint 1 at 0x14001fdd0
(gdb) r
Starting program: C:\qiewer\heob\heob64.exe
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x3dbf4120
Cannot insert breakpoint 1.
Cannot access memory at address 0x77644120
```

The problem doesn't exist in gdb 13.2, and the difference can easily be
seen when printing ExitProcess.
gdb 14.1:
```
(gdb) p ExitProcess
$1 = {<text variable, no debug info>} 0x77644120 <UserHandleGrantAccess+36128>
```
gdb 13.2:
```
(gdb) p ExitProcess
$1 = {<text variable, no debug info>} 0x77734120 <ntdll!RtlExitUserProcess>
```

The new behavior started with 9675da25357c7a3f472731ddc6eb3becc65b469a,
where VMA was then calculated relative to FORWARD_DLL_NAME, while it was
relative to DLL_NAME before.

Fixed by calculating VMA relative to DLL_NAME again.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31112
Approved-By: Tom Tromey <tom@tromey.com>
1 file changed