configure: disable static linking on Darwin

Static liunking is not supported on Darwin, so hide the corresponding
options when the build machine is Darwin.

Reported-by: Andrea Franceschini <therealmorpheu5@gmail.com>
Reported-by: Bryan Hundven <bryanhundven@gmail.com>
Reported-by: "Titus von Boxberg" <titus@v9g.de>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # powerpc specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_SUPPORTS_64 if EXPERIMENTAL

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORT_ABI

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ##

 ## help The PowerPC architecture, as defined by:

 ## help     http://www.ibm.com/developerworks/eserver/articles/archguide.html