Upgrade gcc-10 to gcc-11 in Appveyor CI.

appveyor.yml

@@ -7,16 +7,16 @@ install:
 - sh: >-
     if test "${APPVEYOR_BUILD_WORKER_IMAGE}" = "Ubuntu"; then
         sudo apt-get update -y
-        sudo apt-get install -y gcc-10
+        sudo apt-get install -y gcc-11
     fi
 
 build_script:
 - cc --version
-- if test "${APPVEYOR_BUILD_WORKER_IMAGE}" = "Ubuntu"; then gcc-10 --version; fi
+- if test "${APPVEYOR_BUILD_WORKER_IMAGE}" = "Ubuntu"; then gcc-11 --version; fi
 
 test_script:
 - make -C tests EXTRA_CFLAGS="-Wextra -Wswitch-default -Wno-type-limits"
-- if test "${APPVEYOR_BUILD_WORKER_IMAGE}" = "Ubuntu"; then make -C tests clean ; make -C tests CC=gcc-10 EXTRA_CFLAGS="--analyzer"; fi
+- if test "${APPVEYOR_BUILD_WORKER_IMAGE}" = "Ubuntu"; then make -C tests clean ; make -C tests CC=gcc-11 EXTRA_CFLAGS="--analyzer"; fi
 - make -C tests clean ; make -C tests pedantic
 - make -C tests clean ; make -C tests pedantic EXTRA_CFLAGS=-DNO_DECLTYPE
 - make -C tests clean ; make -C tests cplusplus