Makefile: set SHELL to value of SHELL_PATH

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1060,6 +1060,8 @@ export TAR INSTALL DESTDIR SHELL_PATH
 
 ### Build rules
 
+SHELL = $(SHELL_PATH)
+
 all:: $(ALL_PROGRAMS) $(BUILT_INS) $(OTHER_PROGRAMS) GIT-BUILD-OPTIONS
 ifneq (,$X)
 	$(foreach p,$(patsubst %$X,%,$(filter %$X,$(ALL_PROGRAMS) $(BUILT_INS) git$X)), $(RM) '$p';)