Reduce some of GCC 7's nagging

Add fallthrough comments to tinyformat.hpp to disable
-Wimplicit-fallthrough warnings.

Also disable -Wattributes in embree, since it generates a lot of
warnings from that.

CMakeLists.txt

@@ -79,7 +79,7 @@ add_library(thirdparty STATIC
 		src/thirdparty/skylight/ArHosekSkyModel.cpp)
 
 if (CMAKE_COMPILER_IS_GNUCXX)
-    set(CXX_WARNINGS "-Wall -Wextra -Wpointer-arith -Wcast-align -fstrict-aliasing -Wno-unused-local-typedefs -Wno-misleading-indentation -Wno-maybe-uninitialized")
+    set(CXX_WARNINGS "-Wall -Wextra -Wpointer-arith -Wcast-align -fstrict-aliasing -Wno-unused-local-typedefs -Wno-misleading-indentation -Wno-maybe-uninitialized -Wno-implicit-fallthrough")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXX_WARNINGS} -fvisibility-inlines-hidden")
 endif()
 set(core_libs core thirdparty embree)

src/thirdparty/embree/common/cmake/gcc.cmake

@@ -24,7 +24,7 @@ SET(FLAGS_AVX2  "-mf16c -mavx2 -mfma -mlzcnt -mbmi -mbmi2")
 SET(FLAGS_AVX512KNL "-mavx512f -mavx512pf -mavx512er -mavx512cd")
 SET(FLAGS_AVX512SKX "-mavx512f -mavx512dq -mavx512cd -mavx512bw -mavx512vl")
 
-SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fPIC -std=c++11 -fvisibility-inlines-hidden -fvisibility=hidden -fno-strict-aliasing -Wno-misleading-indentation -Wno-parentheses -Wno-unused-variable -Wno-unused-but-set-variable -Wno-sign-compare -Wno-maybe-uninitialized -Wno-terminate")
+SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fPIC -std=c++11 -fvisibility-inlines-hidden -fvisibility=hidden -fno-strict-aliasing -Wno-misleading-indentation -Wno-parentheses -Wno-unused-variable -Wno-unused-but-set-variable -Wno-sign-compare -Wno-maybe-uninitialized -Wno-terminate -Wno-attributes")
 SET(CMAKE_CXX_FLAGS_DEBUG          "-DDEBUG  -DTBB_USE_DEBUG -g -O0")
 SET(CMAKE_CXX_FLAGS_RELEASE        "-DNDEBUG                    -O3")
 SET(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-DDEBUG  -DTBB_USE_DEBUG -g -O3")