change alpine install script

Author: lerman25

.install/alpine_linux_3.sh

@@ -1,9 +1,14 @@
 #!/bin/bash
-MODE=$1 # whether to install using sudo or not
+MODE=$1
 set -e
 
 $MODE apk update
+$MODE apk add --no-cache build-base gcc g++ make wget git valgrind linux-headers cmake
 
-$MODE apk add --no-cache build-base gcc g++ make wget git valgrind linux-headers
+# Force C++17 and prevent the C++20 deprecation from being a hard error
+export CXXFLAGS="$CXXFLAGS -std=gnu++17 -Wno-error=deprecated -Wno-error=deprecated-declarations"
+export CFLAGS="$CFLAGS -std=gnu++17"
 
-$MODE apk add --no-cache cmake
+# (Optional) persist for subsequent CI steps/shells
+echo 'export CXXFLAGS="$CXXFLAGS -std=gnu++17 -Wno-error=deprecated -Wno-error=deprecated-declarations"' | $MODE tee /etc/profile.d/cpp17.sh >/dev/null
+echo 'export CFLAGS="$CFLAGS -std=gnu++17"' | $MODE tee -a /etc/profile.d/cpp17.sh >/dev/null