t/Makefile: Can't include GIT-BUILD-OPTIONS, it's a .sh

Change the smoke testing portion of t/Makefile not to include
GIT-BUILD-OPTIONS. It's a shellscript, not a Makefile snippet, so it
had the nasty side-effect of sneaking e.g. SHELL_PATH = '/bin/sh'
(with quotes) everywhere.

Just add our own PERL_PATH variable as a workaround. The t/Makefile
already has e.g. an equivalent SHELL_PATH and TAR option which
duplicate the definitions in GIT-BUILD-OPTIONS.
Reported-by: NThomas Rast <trast@student.ethz.ch>
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/Makefile

@@ -8,6 +8,7 @@
 
 #GIT_TEST_OPTS=--verbose --debug
 SHELL_PATH ?= $(SHELL)
+PERL_PATH ?= /usr/bin/perl
 TAR ?= $(TAR)
 RM ?= rm -f
 
@@ -50,7 +51,6 @@ valgrind:
 	GIT_TEST_OPTS=--valgrind $(MAKE)
 
 # Smoke testing targets
--include ../GIT-BUILD-OPTIONS
 -include ../GIT-VERSION-FILE
 uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo unknown')
 uname_M := $(shell sh -c 'uname -m 2>/dev/null || echo unknown')