scripts: Use gtimeout instead of timeout when available (#260).

Before this commit, retdec-archive-decompiler.sh on macOS failed with the
following error:

    $ retdec-archive-decompiler.sh
    error: The `timeout` command is required but it is not available. Aborting.

The reason for this is that on macOS, timeout from GNU coreutils is installed
as gtimeout (unless you have installed coreutils with `brew install coreutils
--with-default-names`).

The present commit updates the script so it uses gtimeout when available (we
already do the same for e.g. greadlink and gha256sum).

scripts/retdec-archive-decompiler.sh

@@ -3,10 +3,6 @@
 # Runs the decompilation script with the given arguments over all files in the
 # given static library.
 #
-# Requirements:
-#  - bash
-#  - the `timeout` command
-#
 
 # On macOS, we want the GNU version of 'readlink', which is available under
 # 'greadlink':
@@ -27,17 +23,6 @@ fi
 
 . "$DECOMPILER_UTILS"
 
-##
-## Check that all script requirements are satisfied.
-##
-for CMD in "timeout"; do
-	command -v $CMD > /dev/null 2>&1 || {
-		echo "error: The \`$CMD\` command is required but it is not" \
-			"available. Aborting." >&2
-		exit 1
-	}
-done
-
 ##
 ## Configuration.
 ##
@@ -187,7 +172,7 @@ for ((INDEX=0; INDEX<FILE_COUNT; INDEX++)); do
 
 	# We have to use indexes instead of names because archives can contain multiple files with same name.
 	LOG_FILE="$LIBRARY_PATH.file_$FILE_INDEX.log.verbose"                                                    # Do not escape!
-	timeout $TIMEOUT "$DECOMPILE_SH" --ar-index="$INDEX" -o "$LIBRARY_PATH.file_$FILE_INDEX" "$LIBRARY_PATH" $DECOMPILE_SH_ARGS > "$LOG_FILE" 2>&1
+	gnutimeout $TIMEOUT "$DECOMPILE_SH" --ar-index="$INDEX" -o "$LIBRARY_PATH.file_$FILE_INDEX" "$LIBRARY_PATH" $DECOMPILE_SH_ARGS > "$LOG_FILE" 2>&1
 	RC=$?
 
 	# Print status.

scripts/retdec-utils.sh

@@ -22,6 +22,17 @@ fi
 
 . "$DECOMPILER_CONFIG"
 
+# On macOS, 'timeout' from GNU coreutils is by default available under
+# 'gtimeout'.
+gnutimeout()
+{
+	if hash gtimeout 2> /dev/null; then
+		gtimeout "$@"
+	else
+		timeout "$@"
+	fi
+}
+
 #
 # Prints the real, physical location of a directory or file, relative or
 # absolute.