perf tests: Adding build test for having ending double slash

Pawel Moll reported build issue for having extra slash (/) at the end of
the prefix variable.

  $ make prefix=/usr/local/

    CC       tests/attr.o
  tests/attr.c: In function ‘test__attr’:
  tests/attr.c:168:50: error: expected ‘)’ before ‘;’ token
    snprintf(path_perf, PATH_MAX, "%s/perf", BINDIR);
                                                ^
  tests/attr.c:176:1: error: expected ‘;’ before ‘}’ token
   }
   ^
  tests/attr.c:176:1: error: control reaches end of non-void function [-Werror=return-type]
   }
   ^
  cc1: all warnings being treated as errors

Adding automated test case for this.
Reported-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20150727182417.GD20509@krava.brq.redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/make

@@ -58,7 +58,8 @@ make_install_man    := install-man
 make_install_html   := install-html
 make_install_info   := install-info
 make_install_pdf    := install-pdf
-make_install_prefix := install prefix=/tmp/krava
+make_install_prefix       := install prefix=/tmp/krava
+make_install_prefix_slash := install prefix=/tmp/krava/
 make_static         := LDFLAGS=-static
 
 # all the NO_* variable combined
@@ -101,6 +102,7 @@ run += make_util_pmu_bison_o
 run += make_install
 run += make_install_bin
 run += make_install_prefix
+run += make_install_prefix_slash
 # FIXME 'install-*' commented out till they're fixed
 # run += make_install_doc
 # run += make_install_man
@@ -175,11 +177,14 @@ test_make_install_O     := $(call test_dest_files,$(installed_files_all))
 test_make_install_bin   := $(call test_dest_files,$(installed_files_bin))
 test_make_install_bin_O := $(call test_dest_files,$(installed_files_bin))
 
-# We prefix all installed files for make_install_prefix
+# We prefix all installed files for make_install_prefix(_slash)
 # with '/tmp/krava' to match installed/prefix-ed files.
 installed_files_all_prefix := $(addprefix /tmp/krava/,$(installed_files_all))
-test_make_install_prefix   := $(call test_dest_files,$(installed_files_all_prefix))
-test_make_install_prefix_O := $(call test_dest_files,$(installed_files_all_prefix))
+test_make_install_prefix   :=  $(call test_dest_files,$(installed_files_all_prefix))
+test_make_install_prefix_O :=  $(call test_dest_files,$(installed_files_all_prefix))
+
+test_make_install_prefix_slash   := $(test_make_install_prefix)
+test_make_install_prefix_slash_O := $(test_make_install_prefix_O)
 
 # FIXME nothing gets installed
 test_make_install_man    := test -f $$TMP_DEST/share/man/man1/perf.1