Update build.sh for gcc-5 on arch

if /etc/arch-release then we will check for gcc5 and use it if found, otherwise we will error out due to failed deps

zcutil/build.sh

@@ -96,6 +96,18 @@ then
     shift
 fi
 
+# Arch workaround for gcc 7
+# might break the entry above to find gcc- on arm
+if [ -f "/etc/arch-release" ]; then
+    if [ -f "/usr/bin/gcc-5" ]; then
+    CC=gcc-5
+    CXX=g++-5
+    fi
+else
+echo 'gcc5 required, please install using "sudo pacman -S gss5"'
+exit 1
+fi
+
 PREFIX="$(pwd)/depends/$BUILD/"
 
 eval "$MAKE" --version