Build: Added option to treat warnings as errors

Useful for CI.

Change-Id: I68b5acc949de69f1f7fb502bdc8efbbb659c3155
Signed-off-by: Bohdan Hunko <Bohdan.Hunko@infineon.com>
diff --git a/toolchain_GNUARM.cmake b/toolchain_GNUARM.cmake
index 074fac4..9d3ae09 100644
--- a/toolchain_GNUARM.cmake
+++ b/toolchain_GNUARM.cmake
@@ -123,6 +123,7 @@
     $<$<COMPILE_LANGUAGE:C>:-std=c99>
     $<$<COMPILE_LANGUAGE:CXX>:-std=c++11>
     $<$<OR:$<BOOL:${TFM_DEBUG_SYMBOLS}>,$<BOOL:${TFM_CODE_COVERAGE}>>:-g>
+    $<$<AND:$<COMPILE_LANGUAGE:C,CXX>,$<BOOL:${CONFIG_TFM_WARNINGS_ARE_ERRORS}>>:-Werror>
 )
 
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