test_common: fix -Wsign-compare warnings (#1759)

In preparation of re-enabling `-Wsign-compare` globally, avoid mixing
signed and unsigned integers in comparisons in test_common.

Signed-off-by: Sven van Haastregt <sven.vanhaastregt@arm.com>

test_common/gl/helpers.cpp

@@ -1715,7 +1715,7 @@ void * CreateGLRenderbuffer( GLsizei width, GLsizei height,
  // Reverse and reorder to validate since in the
  // kernel the read_imagef() call always returns RGBA
  cl_uchar *p = (cl_uchar *)buffer;
- for( size_t i = 0; i < (size_t)width * height; i++ )
+ for (GLsizei i = 0; i < width * height; i++)
  {
  cl_uchar uc0 = p[i * 4 + 0];
  cl_uchar uc1 = p[i * 4 + 1];
@@ -1733,7 +1733,7 @@ void * CreateGLRenderbuffer( GLsizei width, GLsizei height,
  // Reverse and reorder to validate since in the
  // kernel the read_imagef() call always returns RGBA
  cl_uchar *p = (cl_uchar *)buffer;
- for( size_t i = 0; i < width * height; i++ )
+ for (GLsizei i = 0; i < width * height; i++)
  {
  cl_uchar uc0 = p[i * 4 + 0];
  cl_uchar uc1 = p[i * 4 + 1];

test_common/harness/testHarness.cpp

@@ -835,9 +835,9 @@ void callTestFunctions(test_definition testList[],
  std::vector<std::thread *> threads;
  test_harness_state state = { testList, resultTestList, deviceToUse,
  config };
- for (int i = 0; i < config.numWorkerThreads; i++)
+ for (unsigned i = 0; i < config.numWorkerThreads; i++)
  {
- log_info("Spawning worker thread %i\n", i);
+ log_info("Spawning worker thread %u\n", i);
  threads.push_back(new std::thread(test_function_runner, &state));
  }