This is perhaps worth at least raising for developer documentation. I managed with @a.harker 's help to build FrameLib for the M1 architecture. It is relatively simple to do - you just need to change some of the Xcode configurations.
Below is the diff of my .xcconfig
diff --git a/Config_FrameLib.xcconfig b/Config_FrameLib.xcconfig
index fa6074da..ae7ea8b1 100755
--- a/Config_FrameLib.xcconfig
+++ b/Config_FrameLib.xcconfig
@@ -5,12 +5,12 @@ PRODUCT_NAME = $(TARGET_NAME)
// Per architecture and deployment settings
-ARCHS = i386 x86_64
+ARCHS = x86_64
-MACOSX_DEPLOYMENT_TARGET = 10.7
+MACOSX_DEPLOYMENT_TARGET = 11.1
CLANG_CXX_LANGUAGE_STANDARD = c++11
CLANG_CXX_LIBRARY = libc++
-CLANG_X86_VECTOR_INSTRUCTIONS = avx
+CLANG_X86_VECTOR_INSTRUCTIONS = sse4.2
LLVM_LTO = Monolithic
Very simple!