test cases: make various things werror-safe

Allows getting closer to `./run_project_tests.py -- -Dwerror=true`.

- when argc and argv are not *both* used, there's a standard, compliant
  mechanism to mark the variable as unused
- generated code should not build as -Werror
- more thoroughly comment out some commented code

test cases/common/117 shared module/meson.build

@@ -36,5 +36,6 @@ test('import test 2', e, args : m2)
 
 # Shared module that does not export any symbols
 shared_module('nosyms', 'nosyms.c',
+  override_options: ['werror=false'],
   install : true,
   install_dir : join_paths(get_option('libdir'), 'modules'))

test cases/common/147 simd/simd_mmx.c

@@ -45,14 +45,16 @@ void increment_mmx(float arr[4]) {
      * enough to fit in int16;
      */
     int i;
+    /* This is unused due to below comment about GCC 8.
     __m64 packed = _mm_set_pi16(arr[3], arr[2], arr[1], arr[0]);
     __m64 incr = _mm_set1_pi16(1);
     __m64 result = _mm_add_pi16(packed, incr);
-    /* Should be
+    int64_t unpacker = (int64_t)(result);
+     */
+    /* The above should be
      * int64_t unpacker = _m_to_int64(result);
      * but it does not exist on 32 bit platforms for some reason.
      */
-    int64_t unpacker = (int64_t)(result);
     _mm_empty();
     for(i=0; i<4; i++) {
       /* This fails on GCC 8 when optimizations are enabled.

test cases/common/148 shared module resolving symbol in executable/prog.c

@@ -30,7 +30,7 @@ int main(int argc, char **argv)
   int expected, actual;
   fptr importedfunc;
 
-  if (argc=0) {};  // noop
+  (void)argc;  // noop
 
 #ifdef _WIN32
   HMODULE h = LoadLibraryA(argv[1]);

test cases/common/245 custom target index source/main.c

@@ -1,8 +1,10 @@
 #include <assert.h>
 #include "gen.h"
 
-int main(int argc)
+int main(int argc, char **argv)
 {
+  (void)argv;
+
   assert(argc == 3);
   return genfunc();
 }

test cases/rust/12 bindgen/dependencies/meson.build

@@ -12,6 +12,8 @@ external_dep_rs = rust.bindgen(
 external_dep = static_library(
   'external_dep',
   [external_dep_rs],
+  # for generated code, do not lint
+  rust_args: ['-A', 'warnings'],
   dependencies : dep_zlib.partial_dependency(links : true),
 )