Fix generate_build_files.py.

third_party/fiat/p256.c is weird. We need to switch everything to
sources.cmake.

Change-Id: I52e56e87a1ac5534b88a372ad68a1052fb019b67
Reviewed-on: https://boringssl-review.googlesource.com/24084
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

util/generate_build_files.py

@@ -594,6 +594,12 @@ def main(platforms):
   tool_c_files = FindCFiles(os.path.join('src', 'tool'), NoTests)
   tool_h_files = FindHeaderFiles(os.path.join('src', 'tool'), AllFiles)
 
+  # third_party/fiat/p256.c lives in third_party/fiat, but it is a FIPS
+  # fragment, not a normal source file.
+  p256 = os.path.join('src', 'third_party', 'fiat', 'p256.c')
+  fips_fragments.append(p256)
+  crypto_c_files.remove(p256)
+
   # Generate err_data.c
   with open('err_data.c', 'w+') as err_data:
     subprocess.check_call(['go', 'run', 'err_data_generate.go'],