Turn on -Wextra

Add -Wextra and silence all warnings with -Wno-*.  Among them, we probably
want to fix

        -Wunused-variable
        -Wunused-but-set-variable
        -Wtype-limits

at some point.

CMakeLists.txt

@@ -25,10 +25,18 @@ if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
 
     set(warning_flags
         -Wall
+        -Wextra
         -Werror
-        -Wno-unused
+        -Wno-unused-variable
+        -Wno-type-limits
+        -Wno-unused-parameter
+        -Wno-missing-field-initializers
         -Wno-unknown-pragmas
         -Wno-reorder)
+    if(CMAKE_COMPILER_IS_GNUCXX)
+        list(APPEND warning_flags -Wno-unused-but-set-variable)
+    endif()
+
     string(REPLACE ";" " " warning_flags "${warning_flags}")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${warning_flags}")
 endif()

renderdoc/CMakeLists.txt

@@ -134,6 +134,11 @@ if(UNIX)
     list(APPEND sources os/linux/linux_libentry.cpp)
 endif()
 
+if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    set_source_files_properties(3rdparty/tinyexr/tinyexr.cpp
+        PROPERTIES COMPILE_FLAGS "-Wno-extra -Wno-unused-function")
+endif()
+
 add_library(rdoc OBJECT ${sources})
 target_compile_definitions(rdoc ${RDOC_DEFINITIONS})
 target_include_directories(rdoc ${RDOC_INCLUDES})