Add explanatory comment to fuzzer build files

This change adds a comment related to the use of host_toolchain to
account for cross compilation, and removes a print statement that had
been accidentally left in a build script.

Bug: tint:966
Change-Id: I6334225864632d9983ab197bb28fcb972d5ba1d4
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/58000
Auto-Submit: Alastair Donaldson <afdx@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

fuzzers/BUILD.gn

@@ -31,11 +31,13 @@ if (build_with_chromium) {
 
   fuzzer_corpus_spirv_dir = "${target_gen_dir}/fuzzer_corpus_spirv"
   action("tint_generate_spirv_corpus") {
-
+    # The spirv-as tool is used to turn SPIR-V assembly files into binary form.
+    # When cross compiling, it is important that spirv-as is built for the
+    # *host* tool chain, and that the host version of spirv-as is used to
+    # prepare the corpus.
     spirv_as_target = "${tint_spirv_tools_dir}/:spirv-as(${host_toolchain})"
     spirv_as_out_dir = get_label_info(spirv_as_target, "root_out_dir")
     deps = [ spirv_as_target ]
-
     script = "generate_spirv_corpus.py"
     sources = [ "generate_spirv_corpus.py" ]
     args = [ rebase_path("${tint_root_dir}/test", root_build_dir), rebase_path(fuzzer_corpus_spirv_dir, root_build_dir), rebase_path("${spirv_as_out_dir}/spirv-as", root_build_dir) ]

fuzzers/generate_spirv_corpus.py

@@ -49,7 +49,6 @@ def main():
     input_dir: str = os.path.abspath(sys.argv[1].rstrip(os.sep))
     corpus_dir: str = os.path.abspath(sys.argv[2])
     spirv_as_path: str = os.path.abspath(sys.argv[3])
-    print(' '.join([input_dir, corpus_dir, spirv_as_path]))
     if os.path.exists(corpus_dir):
         shutil.rmtree(corpus_dir)
     os.makedirs(corpus_dir)