libunwind: fix architecture dependencies

libunwind: fix architecture dependencies

Due to a misplaced parenthesis, the libunwind dependency were
incorrect. Indeed, they were of the form:

 default y if LIBC_TYPE && (arm dependency) || (list of other architectures)

Which meant that that the LIBC_TYPE dependency was not taken into
account for the "other architectures". This commit changes that to:

 default y if LIBC_TYPE && ((arm dependency) || list of other architectures)

Without this fix, libunwind can be selected for example on
PowerPC/uClibc configurations, while only PowerPC/glibc should be
allowed. This fixes:

  http://autobuild.buildroot.net/results/96c53ff240dcd68fcc9e3d32c4026c9886edcbe7/

Similarly, it also fixes cases where SuperH/uClibc was allowed, while
only SuperH/glibc should be allowed. This fixes:

  http://autobuild.buildroot.net/results/95a6cca21aea9914ba8bb3f571760fc054c53ecd/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>