Top level Makefile generated by ./configure contained a hard coded

SHELL=/bin/sh which isn't appropriate for OS/2. Make it find sh in the
PATH if /bin/sh doesn't exist.

Reviewed by:	Ralf S. Engelschall


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83017 13f79535-47bb-0310-9956-ffa450edef68