COMPMID-2177 Fix clang warnings

Change-Id: I78039db8c58d7b14a042c41e54c25fb9cb509bf7
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/1092
Reviewed-by: VidhyaSudhan Loganathan <vidhyasudhan.loganathan@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/core/GLES_COMPUTE/GCKernelLibrary.cpp b/src/core/GLES_COMPUTE/GCKernelLibrary.cpp
index 25ac02e..0af8c7d 100644
--- a/src/core/GLES_COMPUTE/GCKernelLibrary.cpp
+++ b/src/core/GLES_COMPUTE/GCKernelLibrary.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018 ARM Limited.
+ * Copyright (c) 2017-2019 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -387,7 +387,7 @@
     return kernel;
 }
 
-const std::string GCKernelLibrary::preprocess_shader(const std::string &shader_source) const
+std::string GCKernelLibrary::preprocess_shader(const std::string &shader_source) const
 {
     enum class ParserStage
     {
@@ -399,7 +399,7 @@
 
     // Define a GLES compute shader parser function
     std::function<std::string(const std::string &, ParserStage, int)> cs_parser;
-    cs_parser = [&](const std::string & src, ParserStage stage, int nested_level) -> std::string
+    cs_parser = [&](const std::string & src, ParserStage stage, int) -> std::string
     {
         std::string dst;