[client] tests: dont use fast math

Clang C and C++ produce slightly different powf rounding with fast math,
for testing disable it.

client/tests/CMakeLists.txt

@@ -49,6 +49,10 @@ set_target_properties(render-tests PROPERTIES
   CXX_STANDARD_REQUIRED ON
 )
 
+target_compile_options(render-tests PRIVATE
+  -fno-fast-math
+)
+
 target_compile_definitions(render-tests PRIVATE
   LG_CLIENT_PATH="$<TARGET_FILE:looking-glass-client>"
 )