-m64 doesn't work?

[Andre Tampubolon]

When I was looking at dmd's options, I found this:
m64 generate 64 bit code

I guessed it behaves like gcc (m64 for 64 bit code and m32 for 32 bit code, assuming you have the multilibs), so I did a rebuild.
This is the structure of my /opt/dmd-dev
 
   |-bin (64-bit version of dmd, impcnvgen, idgen, optabgen, plus dmd.conf)
   |-import
   |---core
   |-----stdc
   |-----sync
   |-----sys
   |-------osx
   |---------mach
   |-------posix
   |---------arpa
   |---------net
   |---------netinet
   |---------sys
   |-------windows
   |-lib32 (libdruntime-linux32.a and libphobos.a)
   |-lib64 (libdruntime-linux64.a and libphobos.a)
   |-phobos
   |---std
   |-----c
   |-------freebsd
   |-------linux
   |-------osx
   |-------windows
   |-----internal
   |-------math
   |-------windows
   |-----net
   |-----windows

And this is my dmd.conf:
[Environment]
DFLAGS=-I/opt/dmd-dev/import -I/opt/dmd-dev/phobos -L-L/opt/dmd-dev/lib32 -L-L/opt/dmd-dev/lib64

dmd -32 works fine. But either dmd or dmd -m64 doesn't work, e.g:
$ dmd -m64 einstein2b.d
/usr/bin/ld: skipping incompatible /opt/dmd-dev/lib32//libphobos2.a when searching for -lphobos2
/usr/bin/ld: cannot find -lphobos2
collect2: ld returned 1 exit status
--- errorlevel 1

I wonder why ld searches at /opt/dmd-dev/lib32, whereas it should be /opt/dmd-dev/lib64 ?