Fix out-of-source ‘make check’ emacs-module-tests

Problem reported by Koki Fukuda in:
https://lists.gnu.org/r/emacs-devel/2020-07/msg00169.html
* test/Makefile.in (MODULE_CFLAGS):
Include from the same directories included from in ../src.
* test/src/emacs-module-tests.el (module/describe-function-1):
Strip path to source directory.

(cherry picked from commit c86f3fe0d0)

test/Makefile.in

@@ -258,9 +258,7 @@ endif
 GMP_LIB = @GMP_LIB@
 GMP_OBJ = $(if @GMP_OBJ@, ../src/@GMP_OBJ@)
 
-# Note: emacs-module.h is generated from emacs-module.h.in, hence we
-# look in ../src, not $(srcdir)/../src.
-MODULE_CFLAGS = -I../src -I$(srcdir)/../lib \
+MODULE_CFLAGS = -I../src -I$(srcdir)/../src -I../lib -I$(srcdir)/../lib \
   $(FPIC_CFLAGS) $(PROFILING_CFLAGS) \
   $(WARN_CFLAGS) $(WERROR_CFLAGS) $(CFLAGS)
 

test/src/emacs-module-tests.el

@@ -318,6 +318,9 @@ local reference."
   (with-temp-buffer
     (let ((standard-output (current-buffer)))
       (describe-function-1 #'mod-test-sum)
+      (goto-char (point-min))
+      (while (re-search-forward "`[^']*/data/emacs-module/" nil t)
+        (replace-match "`data/emacs-module/"))
       (should (equal
                (buffer-substring-no-properties 1 (point-max))
                (format "a module function in `data/emacs-module/mod-test%s'.