setup scripts: do not use sudo if already running under root

Reworked variant of #4753.

Copied from 99236ea commit in `master` branch.

scripts/setup-archlinux.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -e -u
 
 PACKAGES=""
@@ -43,9 +43,16 @@ PACKAGES+=" lua" # Needed to build luarocks package.
 PACKAGES+=" python-recommonmark" # Needed for LLVM-8 documentation.
 PACKAGES+=" jre8-openjdk-headless"
 
-sudo pacman -Syq --noconfirm $PACKAGES
+# Do not require sudo if already running as root.
+if [ "$(id -u)" = "0" ]; then
+	SUDO=""
+else
+	SUDO="sudo"
+fi
 
-sudo mkdir -p /data/data/com.termux/files/usr
-sudo chown -R $(whoami) /data
+$SUDO pacman -Syq --noconfirm $PACKAGES
+
+$SUDO mkdir -p /data/data/com.termux/files/usr
+$SUDO chown -R $(whoami) /data
 
 echo "Please also install ncurses5-compat-libs and makedepend packages from the AUR before continuing"

scripts/setup-ubuntu.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -e -u
 
 PACKAGES=""
@@ -57,11 +57,18 @@ PACKAGES+=" zip" # For smalltalk.
 PACKAGES+=" libssl-dev:i386" # Needed by swi-prolog 32-bit
 PACKAGES+=" zlib1g-dev:i386"
 
+# Do not require sudo if already running as root.
+if [ "$(id -u)" = "0" ]; then
+	SUDO=""
+else
+	SUDO="sudo"
+fi
+
 # Allow 32-bit packages.
-sudo dpkg --add-architecture i386
-sudo apt-get -yq update
+$SUDO dpkg --add-architecture i386
+$SUDO apt-get -yq update
 
-sudo DEBIAN_FRONTEND=noninteractive \
+$SUDO DEBIAN_FRONTEND=noninteractive \
 	apt-get install -yq --no-install-recommends $PACKAGES
 
 # Find and assign UBUNTU_VERSION
@@ -76,8 +83,8 @@ curl -O http://security.ubuntu.com/ubuntu/pool/universe/o/openjdk-8/openjdk-8-jd
 curl -O http://security.ubuntu.com/ubuntu/pool/universe/o/openjdk-8/openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb
 curl -O http://security.ubuntu.com/ubuntu/pool/universe/o/openjdk-8/openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb
 curl -O http://security.ubuntu.com/ubuntu/pool/universe/o/openjdk-8/openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb
-sudo dpkg -i openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb || sudo apt install -f -y
+$SUDO dpkg -i openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb || $SUDO apt install -f -y
 rm openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb
 
-sudo mkdir -p /data/data/com.termux/files/usr
-sudo chown -R $(whoami) /data
+$SUDO mkdir -p /data/data/com.termux/files/usr
+$SUDO chown -R $(whoami) /data