Strange linker problems

[Benjamin Thaut]

I have a strange problem with gdc. The linker reports undefined 
references to symbols, but exactly those symbols exist in the library 
that I'm linking into the executable. The error message I get is:

C:\Users\Benjamin\AppData\Local\Temp\cc4pUOfp.o:main.d:(.text+0x3a): 
undefined reference to `_D6thBase2io8writeflnFAyaYm'

But:

nm libthBase64d_mingw.a | grep writefln
000000000003c9b2 T _D6thBase2io8writeflnFAyaYm

I'm building with:

gdc -m64 
-I"C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\druntime\import" 
-I"C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos" 
-I"C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\thBase\src" 
-fversion=NOGCSAFE -o "test.exe" 
-L"C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos" 
-L. -lthBase64d_mingw -debuglib=phobosnogc64d_mingw -Wl,--verbose=2 
-defaultlib=phobosnogc64d_mingw -v -pipe -nostdinc main.d

The verbose output of the linker also shows that it finds the correct 
library file:

attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/libthBase64d_mingw.dll.a 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/thBase64d_mingw.dll.a 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/libthBase64d_mingw.a 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/thBase64d_mingw.lib 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/libthBase64d_mingw.dll 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos/thBase64d_mingw.dll 
failed
attempt to open 
C:\Users\Benjamin\Documents\d-projects\Spacecraft-git\game\..\..\phobos\libthBase64d_mingw.a 
failed
attempt to open ./libthBase64d_mingw.dll.a failed
attempt to open ./thBase64d_mingw.dll.a failed
attempt to open ./libthBase64d_mingw.a succeeded

Any ideas what is going wrong here?

Kind Regards
Benjamin Thaut