CMakeLists.txt: Set -fno-strict-aliasing for basisu

Several basisu headers demand doing this ("Important: If compiling with
 gcc, be sure strict aliasing is disabled: -fno-strict-aliasing") and
their own CMakeLists.txt (that's not used here) also sets it and
explicitly mentions (in a comment in its first line) that strict
aliasing optimizations must be disabled for both the encoder and decoder

Author: DanielGibson

CMakeLists.txt

@@ -847,7 +847,7 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
         # It's too much work to discriminate which files need which warnings
         # disabled.
         ${BASISU_ENCODER_CXX_SRC}
-        PROPERTIES COMPILE_OPTIONS "-Wno-sign-compare;-Wno-unused-variable;-Wno-class-memaccess;-Wno-misleading-indentation;-Wno-extra;-Wno-deprecated-copy;-Wno-parentheses;-Wno-strict-aliasing"
+        PROPERTIES COMPILE_OPTIONS "-Wno-sign-compare;-Wno-unused-variable;-Wno-class-memaccess;-Wno-misleading-indentation;-Wno-extra;-Wno-deprecated-copy;-Wno-parentheses"
     )
     set_source_files_properties(
         external/basisu/transcoder/basisu_transcoder.cpp
@@ -945,6 +945,26 @@ else()
     message(FATAL_ERROR "${CMAKE_CXX_COMPILER_ID} not yet supported.")
 endif()
 
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
+    # Basis Universal requires strict aliasing to be disabled for GCC and Clang
+    get_source_file_property(cur_options
+        external/basisu/encoder/basisu_comp.cpp
+        COMPILE_OPTIONS
+    )
+    set_source_files_properties(
+        ${BASISU_ENCODER_CXX_SRC}
+        PROPERTIES COMPILE_OPTIONS "${cur_options};-fno-strict-aliasing"
+    )
+    get_source_file_property(cur_options
+        external/basisu/transcoder/basisu_transcoder.cpp
+        COMPILE_OPTIONS
+    )
+    set_source_files_properties(
+        external/basisu/transcoder/basisu_transcoder.cpp
+        PROPERTIES COMPILE_OPTIONS "${cur_options};-fno-strict-aliasing"
+    )
+endif()
+
 # Retrieve the final set of properties for use by the transcodetests.
 # We do this because the CMake feature that would allow the transcodetests
 # target to retrieve these from the ktx target are not available until