configure: Copy mmacosx-version-min option from CFLAGS to WINEPRELOADER_LDFLAGS.

[Piotr Caban]

We fail to link preloader when CFLAGS="-mmacosx-version-min=10.7" 
(because configure check also includes CFLAGS).

Signed-off-by: Piotr Caban <piotr(a)codeweavers.com>
---
  configure.ac | 5 +++++
  1 file changed, 5 insertions(+)