Bugzilla Bug 317620: use "pwd -W" to convert $(DIST) to an absolute

pathname (ABS_DIST) under MSYS on Windows.  We use the same method to
to define MOZ_BUILD_ROOT in configure.in.  The patch is contributed by
Chris Seawood <cls@seawood.org>.  r=wtc.

security/manager/Makefile.in

@@ -123,6 +123,9 @@ ifeq ($(HOST_OS_ARCH),WINNT)
 ifdef CYGDRIVE_MOUNT
 ABS_DIST := $(shell cygpath -w $(ABS_DIST) | sed -e 's|\\|/|g')
 endif
+ifneq (,$(filter mingw%,$(host_os)))
+ABS_DIST := $(shell cd $(DIST) && pwd -W)
+endif
 endif
 NSPR_INCLUDE_DIR = $(firstword $(filter -I%,$(NSPR_CFLAGS)))
 ifneq (,$(strip $(NSPR_INCLUDE_DIR)))