Use bash for default GNU Make shell application

Some Make script commands rely on bash-specific features like brace
expansion, so default to bash for the SHELL variable with a fallback
to the standard sh shell

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

Makefile

@@ -45,7 +45,12 @@ HOSTARCH := $(shell uname -m | \
 HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
 	    sed -e 's/\(cygwin\).*/cygwin/')
 
-export	HOSTARCH HOSTOS
+# Set shell to bash if possible, otherwise fall back to sh
+SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
+	else if [ -x /bin/bash ]; then echo /bin/bash; \
+	else echo sh; fi; fi)
+
+export	HOSTARCH HOSTOS SHELL
 
 # Deal with colliding definitions from tcsh etc.
 VENDOR=