Apple M1: Detect incompatible universal merges

Adds a step to detect when the Intel and arm64 build trees cannot be merged
safely. This can occur when each side has files/folders that are named the same
but are of different types or symlinks that are the same name but need to point
to different locations for each architecture.

Before this change, this would just fail silently.

BuildMacOSUniversalBinary.py

@@ -162,6 +162,32 @@ def recursive_merge_binaries(src0, src1, dst):
        the source trees
     """
 
+    # Check that all files present in the folder are of the same type and that
+    # links link to the same relative location
+    for newpath0 in glob.glob(src0+"/*"):
+        filename = os.path.basename(newpath0)
+        newpath1 = os.path.join(src1, filename)
+        if not os.path.exists(newpath1):
+            continue
+
+        if os.path.islink(newpath0) and os.path.islink(newpath1):
+            if os.path.relpath(newpath0,src0) == os.path.relpath(newpath1,src1):
+                continue
+
+        if os.path.isdir(newpath0) and os.path.isdir(newpath1):
+            continue
+
+        # isfile() can be true for links so check that both are not links
+        # before checking if they are both files
+        if (not os.path.islink(newpath0)) and (not os.path.islink(newpath1)):
+            if os.path.isfile(newpath0) and os.path.isfile(newpath1):
+                continue
+
+        raise Exception(f"{newpath0} and {newpath1} cannot be " +
+                        "merged into a universal binary because they are of " +
+                        "incompatible types. Perhaps the installed libraries" +
+                        " are from different versions for each architecture")
+
     for newpath0 in glob.glob(src0+"/*"):
         filename = os.path.basename(newpath0)
         newpath1 = os.path.join(src1, filename)
@@ -171,7 +197,11 @@ def recursive_merge_binaries(src0, src1, dst):
             continue
 
         if not os.path.exists(newpath1):
-            shutil.copy(newpath0, new_dst_path)
+            if os.path.isdir(newpath0):
+                shutil.copytree(newpath0, new_dst_path)
+            else:
+                shutil.copy(newpath0, new_dst_path)
+
             continue
 
         if os.path.isdir(newpath1):