I have done a scratch build of mono on aarch64, with bootstrap set to 1 and added aarch64 to ExclusiveArch, in the spec file:

%global bootstrap 1
ExclusiveArch: %mono_arches aarch64

Result of the scratch build:
http://arm.koji.fedoraproject.org/koji/taskinfo?taskID=3697357

output in build.log:
Stacktrace:
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Environment.Exit (int) <0x00007>
  at Mono.CSharp.Driver.Main (string[]) <0x0021b>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_int_object (object,intptr,intptr,intptr) <0x000db>
Native stacktrace:
/bin/sh: line 1: 27605 Segmentation fault      (core dumped) MONO_PATH="./../../class/lib/monolite:$MONO_PATH" /builddir/build/BUILD/mono-4.6.0/runtime/mono-wrapper ./../../class/lib/monolite/basic.exe /codepage:65001 -unsafe -nostdlib -nowarn:612,618,1635 -d:INSIDE_CORLIB,MONO_CULTURE_DATA -d:LIBC -d:FEATURE_PAL,GENERICS_WORK,FEATURE_LIST_PREDICATES,FEATURE_SERIALIZATION,FEATURE_ASCII,FEATURE_LATIN1,FEATURE_UTF7,FEATURE_UTF32,MONO_HYBRID_ENCODING_SUPPORT,FEATURE_ASYNC_IO,NEW_EXPERIMENTAL_ASYNC_IO,FEATURE_UTF32,FEATURE_EXCEPTIONDISPATCHINFO,FEATURE_CORRUPTING_EXCEPTIONS,FEATURE_EXCEPTION_NOTIFICATIONS,FEATURE_STRONGNAME_MIGRATION,FEATURE_USE_LCID,FEATURE_FUSION,FEATURE_CRYPTO,FEATURE_X509_SECURESTRINGS,FEATURE_SYNCHRONIZATIONCONTEXT,FEATURE_SYNCHRONIZATIONCONTEXT_WAIT -d:FEATURE_MACL -d:FEATURE_REMOTING,MONO_COM,FEATURE_COMINTEROP,FEATURE_ROLE_BASED_SECURITY -d:MONO_FEATURE_THREAD_ABORT -d:MONO_FEATURE_THREAD_SUSPEND_RESUME -d:MONO_FEATURE_MULTIPLE_APPDOMAINS -d:NET_4_0 -d:NET_4_5 -d:MONO -d:BOOTSTRAP_BASIC -nowarn:1699 -lib:./../../class/lib/basic -optimize /noconfig -d:FEATURE_PAL,GENERICS_WORK,FEATURE_LIST_PREDICATES,FEATURE_SERIALIZATION,FEATURE_ASCII,FEATURE_LATIN1,FEATURE_UTF7,FEATURE_UTF32,MONO_HYBRID_ENCODING_SUPPORT,FEATURE_ASYNC_IO,NEW_EXPERIMENTAL_ASYNC_IO,FEATURE_UTF32,FEATURE_EXCEPTIONDISPATCHINFO,FEATURE_CORRUPTING_EXCEPTIONS,FEATURE_EXCEPTION_NOTIFICATIONS,FEATURE_STRONGNAME_MIGRATION,FEATURE_USE_LCID,FEATURE_FUSION,FEATURE_CRYPTO,FEATURE_X509_SECURESTRINGS,FEATURE_SYNCHRONIZATIONCONTEXT,FEATURE_SYNCHRONIZATIONCONTEXT_WAIT -d:FEATURE_MACL -d:FEATURE_REMOTING,MONO_COM,FEATURE_COMINTEROP,FEATURE_ROLE_BASED_SECURITY -d:MONO_FEATURE_THREAD_ABORT -d:MONO_FEATURE_THREAD_SUSPEND_RESUME -d:MONO_FEATURE_MULTIPLE_APPDOMAINS -resource:resources/charinfo.nlp -resource:resources/collation.core.bin -resource:resources/collation.tailoring.bin -resource:resources/collation.cjkCHS.bin -resource:resources/collation.cjkCHT.bin -resource:resources/collation.cjkJA.bin -resource:resources/collation.cjkKO.bin -resource:resources/collation.cjkKOlv2.bin --runtime:v4 -target:library -out:../../class/lib/basic/mscorlib.dll @corlib.dll.sources
../../build/library.make:279: recipe for target '../../class/lib/basic/mscorlib.dll' failed
make[8]: *** [../../class/lib/basic/mscorlib.dll] Error 139