contrib: update install_db4 to integrate previous backport contents

contains portions of:
- bitcoin@1ac454a
- bitcoin@3352da8
- bitcoin@fac86ac
- bitcoin@8c9b8a3

Co-authored-by: UdjinM6 <UdjinM6@users.noreply.github.com>

contrib/install_db4.sh

@@ -1,19 +1,23 @@
 #!/bin/sh
+# Copyright (c) 2017-2019 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 # Install libdb4.8 (Berkeley DB).
 
+export LC_ALL=C
 set -e
 
 if [ -z "${1}" ]; then
-  echo "Usage: ./install_db4.sh <base-dir> [<extra-bdb-configure-flag> ...]"
+  echo "Usage: $0 <base-dir> [<extra-bdb-configure-flag> ...]"
   echo
   echo "Must specify a single argument: the directory in which db4 will be built."
   echo "This is probably \`pwd\` if you're at the root of the dash repository."
   exit 1
 fi
 
 expand_path() {
-  echo "$(cd "${1}" && pwd -P)"
+  cd "${1}" && pwd -P
 }
 
 BDB_PREFIX="$(expand_path ${1})/db4"; shift;
@@ -22,7 +26,7 @@ BDB_HASH='12edc0df75bf9abd7f82f821795bcee50f42cb2e5f76a6a281b85732798364ef'
 BDB_URL="https://download.oracle.com/berkeley-db/${BDB_VERSION}.tar.gz"
 
 check_exists() {
-  which "$1" >/dev/null 2>&1
+  command -v "$1" >/dev/null
 }
 
 sha256_check() {
@@ -94,7 +98,9 @@ make install
 echo
 echo "db4 build complete."
 echo
+# shellcheck disable=SC2016
 echo 'When compiling dashd, run `./configure` in the following way:'
 echo
 echo "  export BDB_PREFIX='${BDB_PREFIX}'"
+# shellcheck disable=SC2016
 echo '  ./configure BDB_LIBS="-L${BDB_PREFIX}/lib -ldb_cxx-4.8" BDB_CFLAGS="-I${BDB_PREFIX}/include" ...'