cmake: ARM: exclude libunwind in static build

Else error in build with STATIC=ON:

cd /home/redfish/bitmonero/build/release/src/miner && /usr/bin/cmake -E
cmake_link_script CMakeFiles/simpleminer.dir/link.txt --verbose=1
/usr/bin/c++    -std=c++11 -D_GNU_SOURCE  -Wall -Wextra -Wpointer-arith
-Wundef -Wvla -Wwrite-strings -Wno-error=extra
-Wno-error=deprecated-declarations -Wno-unused-parameter
-Wno-unused-variable -Wno-error=unused-variable -Wno-error=undef
-Wno-error=uninitialized -Wlogical-op -Wno-error=maybe-uninitialized
-Wno-reorder -Wno-missing-field-initializers -march=armv7-a
-fno-strict-aliasing -mfloat-abi=hard -DNDEBUG -O2  -flto
-ffat-lto-objects   -static-libgcc -static-libstdc++
-Wl,--wrap=__cxa_throw CMakeFiles/simpleminer.dir/simpleminer.cpp.o  -o
../../bin/simpleminer -rdynamic -Wl,-Bstatic -lrt -Wl,-Bdynamic -ldl
../cryptonote_core/libcryptonote_core.a ../common/libcommon.a
-Wl,-Bstatic -lboost_filesystem -lboost_program_options -lboost_regex
-lboost_chrono -lboost_system -lboost_thread -Wl,-Bdynamic -pthread
-Wl,-Bstatic -lrt -Wl,-Bdynamic -ldl ../blockchain_db/libblockchain_db.a
../cryptonote_core/libcryptonote_core.a
../blockchain_db/libblockchain_db.a
../../contrib/otshell_utils/libotshell_utils.a ../blocks/libblocks.a
../common/libcommon.a ../../external/unbound/libunbound.a -lssl -lcrypto
-lunwind -Wl,-Bstatic -lboost_program_options ../crypto/libcrypto.a
-lboost_date_time -lboost_serialization -lboost_filesystem
../../external/db_drivers/liblmdb/liblmdb.a -Wl,-Bdynamic -pthread
-Wl,-Bstatic -lboost_chrono -lboost_system -lboost_thread -lrt
-Wl,-Bdynamic -ldl
/usr/bin/ld: ../../bin/simpleminer: hidden symbol
`__aeabi_unwind_cpp_pr0' in
/usr/lib/gcc/armv7l-unknown-linux-gnueabihf/6.1.1/libgcc_eh.a(unwind-arm.o)
is referenced by DSO
/usr/bin/ld: final link failed: Bad value
collect2: error: ld returned 1 exit status

CMakeLists.txt

@@ -246,7 +246,8 @@ add_definitions("-DBLOCKCHAIN_DB=${BLOCKCHAIN_DB}")
 
 find_package(Libunwind)
 # Can't install hook in static build on OSX, because OSX linker does not support --wrap
-if(LIBUNWIND_FOUND AND NOT (STATIC AND APPLE))
+# On ARM, having libunwind package (with .so's only) installed breaks static link.
+if(LIBUNWIND_FOUND AND NOT (STATIC AND (APPLE OR ARM6 OR ARM7)))
   set(DEFAULT_STACK_TRACE ON)
 else()
   set(DEFAULT_STACK_TRACE OFF)