CMakeLists: Enabled more clang warnings.

Enable `-Wextra` and `-Wunreachable-code-loop-increment`.
Disable `-Wno-unused-parameter`.

Detects the build warning / breakage fixed by https://swiftshader-review.googlesource.com/c/SwiftShader/+/43989.

Bug: none. Reducing chance of future build breakages.
Change-Id: I3001f0ded71f2f71f817581996cc727e345845a3
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/43991
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Ben Clayton <bclayton@google.com>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e131a13..6601868 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -364,6 +364,8 @@
 
     if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         list(APPEND SWIFTSHADER_COMPILE_OPTIONS
+            "-Wextra"
+            "-Wunreachable-code-loop-increment"
             "-Wunused-lambda-capture"
             "-Wstring-conversion"
             "-Wextra-semi"
@@ -403,6 +405,7 @@
             "-Wno-comment"                        # multi-line comment
             "-Wno-undefined-var-template"         # instantiation of variable 'X' required here, but no definition is available
             "-Wno-extra-semi"                     # extra ';' after member function definition
+            "-Wno-unused-parameter"               # unused parameter 'X'
 
             # Silence errors caused by unknown warnings when building with older
             # versions of Clang. This demands checking that warnings added above