scripts/build: make struct_tags.json deterministic

It's not good to see struct_tags.json change from one build to the next
when nothing changes.

Python's sets are not deterministic, see long story for older commit
f896fc2306 ("scripts: gen_handles: Sort the device handles")

Simply convert multiple_directories to a sorted list before using it.

Fixes commit 80e78208e6 ("kernel: syscalls: no need to include all
syscalls in binary")

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

scripts/build/parse_syscalls.py

@@ -84,6 +84,9 @@ def analyze_headers(include_dir, scan_dir, file_list):
     if scan_dir:
         multiple_directories |= set(scan_dir)
 
+    # Convert to a list to keep the output deterministic
+    multiple_directories = sorted(multiple_directories)
+
     # Look for source files under various directories.
     # Due to "syscalls/*.h" being included unconditionally in various
     # other header files. We must generate the associated syscall