Test: fix Clang missing prototypes warnings harder.

I thought I fixed all in 6b58165856 (which
should have gone into 1c1ded5869 already),
but apparently there were four more instances I missed. Sigh.

src/Magnum/Test/ImageTest.cpp

@@ -206,6 +206,9 @@ namespace Vk {
     }
 
     enum class CompressedPixelFormat { Astc5x5x4RGBAF = 111 };
+    /* Clang -Wmissing-prototypes warns otherwise, even though this is in an
+       anonymous namespace */
+    Vector3i compressedPixelFormatBlockSize(CompressedPixelFormat);
     Vector3i compressedPixelFormatBlockSize(CompressedPixelFormat format) {
         #ifdef CORRADE_NO_ASSERT
         static_cast<void>(format);
@@ -213,6 +216,7 @@ namespace Vk {
         CORRADE_INTERNAL_ASSERT(format == CompressedPixelFormat::Astc5x5x4RGBAF);
         return {5, 5, 4};
     }
+    UnsignedInt compressedPixelFormatBlockDataSize(CompressedPixelFormat);
     UnsignedInt compressedPixelFormatBlockDataSize(CompressedPixelFormat format) {
         #ifdef CORRADE_NO_ASSERT
         static_cast<void>(format);

src/Magnum/Test/ImageViewTest.cpp

@@ -198,6 +198,9 @@ namespace Vk {
     }
 
     enum class CompressedPixelFormat { Astc5x5x4RGBAF = 111 };
+    /* Clang -Wmissing-prototypes warns otherwise, even though this is in an
+       anonymous namespace */
+    Vector3i compressedPixelFormatBlockSize(CompressedPixelFormat);
     Vector3i compressedPixelFormatBlockSize(CompressedPixelFormat format) {
         #ifdef CORRADE_NO_ASSERT
         static_cast<void>(format);
@@ -205,6 +208,7 @@ namespace Vk {
         CORRADE_INTERNAL_ASSERT(format == CompressedPixelFormat::Astc5x5x4RGBAF);
         return {5, 5, 4};
     }
+    UnsignedInt compressedPixelFormatBlockDataSize(CompressedPixelFormat);
     UnsignedInt compressedPixelFormatBlockDataSize(CompressedPixelFormat format) {
         #ifdef CORRADE_NO_ASSERT
         static_cast<void>(format);