Drop an old workaround

This probably isn't necessary when we now use the proper llvm-dlltool
instead of genlib.

Dockerfile

@@ -78,11 +78,6 @@ ENV AS=llvm-as
 ENV NM=llvm-nm
 
 # Build mingw with our freshly built cross compiler
-# Since somewhere between llvm 3.8 and 3.9, SVN rev 273373, git mirror commit
-# d319cd64a4a15,, llvm-ar tries to detect the format (gnu vs bsd) of the
-# existing .a file. For files generated by genlib, it seems to detect the
-# wrong format, leading to lld later segfaulting when trying to link.
-# Force the flag -format gnu to llvm-ar in this step to work around this issue.
 RUN cd mingw-w64/mingw-w64-crt && \
     for arch in armv7 aarch64 i686 x86_64; do \
         mkdir build-$arch && cd build-$arch && \
@@ -101,7 +96,7 @@ RUN cd mingw-w64/mingw-w64-crt && \
             ;; \
         esac && \
         CC=$arch-w64-mingw32-clang \
-        AR="llvm-ar -format gnu" DLLTOOL=llvm-dlltool ../configure --host=$arch-w64-mingw32 --prefix=$TOOLCHAIN_PREFIX/$arch-w64-mingw32 $FLAGS && \
+        AR=llvm-ar DLLTOOL=llvm-dlltool ../configure --host=$arch-w64-mingw32 --prefix=$TOOLCHAIN_PREFIX/$arch-w64-mingw32 $FLAGS && \
         make -j4 && make install && \
         cd .. || exit 1; \
     done