CMake + Gitlab CI: Allow fuzz jobs to pass with warnings

Allow fuzz jobs to pass with warnings because catching warnings is
not their purpose.

Remove -Werror=unused-but-set-variable that was added in
85357ae as a work-around to the fact that -Werror is not
enabled as a side-effect of ENABLE_EXTRA_COMPILER_WARNINGS.

Allow users to control -Werror. For example the MSYS2 build
has many warnings, this policy of adding -Werror= breaks that
build.

.gitlab-ci.yml

@@ -826,7 +826,7 @@ ASan Menagerie Fuzz:
   script:
     - MAX_SECONDS=$(( 4 * 60 * 60 ))
     - printf "\e[0Ksection_start:%s:cmake_section[collapsed=true]\r\e[0KRunning CMake" "$( date +%s)"
-    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=ON -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON ..
+    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=ON -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON -DENABLE_WERROR=Off ..
     - printf "\e[0Ksection_end:%s:cmake_section\r\e[0K" "$( date +%s)"
     - ninja
     - ninja install
@@ -841,7 +841,7 @@ ASan randpkt Fuzz:
   script:
     # XXX Reuse fuzz-asan?
     - printf "\e[0Ksection_start:%s:cmake_section[collapsed=true]\r\e[0KRunning CMake" "$( date +%s)"
-    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=ON -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON ..
+    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=ON -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON -DENABLE_WERROR=Off ..
     - printf "\e[0Ksection_end:%s:cmake_section\r\e[0K" "$( date +%s)"
     - ninja
     - ninja install
@@ -862,7 +862,7 @@ Valgrind Menagerie Fuzz:
     - DEBIAN_FRONTEND=noninteractive apt-get --yes install valgrind
     - MAX_SECONDS=$(( 3 * 60 * 60 ))
     - printf "\e[0Ksection_start:%s:cmake_section[collapsed=true]\r\e[0KRunning CMake" "$( date +%s)"
-    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=OFF -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON ..
+    - cmake -G Ninja -DBUILD_wireshark=OFF -DCMAKE_BUILD_TYPE=Debug -DENABLE_ASAN=OFF -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX -DENABLE_CCACHE=ON -DENABLE_WERROR=Off ..
     - printf "\e[0Ksection_end:%s:cmake_section\r\e[0K" "$( date +%s)"
     - ninja
     - ninja install

CMakeLists.txt

@@ -676,12 +676,6 @@ else() # ! MSVC
 		# code should not introduce new deprecations in any case.
 		#
 		-Wno-error=deprecated-declarations
-		#
-		# GCC < 6.0 had issues with false positives, but current versions
-		# and clang appear to be OK.
-		# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66543
-		#
-		-Werror=unused-but-set-variable
 	)
 
 	#