[SV 17448] Ignore whitespace around $(file ...) names

The other issues related to whitespace reported in this bug are
not addressed by this change.

* src/functions.c (func_file): Strip whitespace from the start and
end of the filename provided to the $(file ...) function.
* tests/scripts/functions/file: Add tests for this.
* tests/test_driver.pl: Use 3-arg version of open().

tests/scripts/functions/file

@@ -23,7 +23,7 @@ define A
 a
 b
 endef
-$(file     >>     file.out,$(A))
+$(file     >>     file.out    ,$(A))
 x:;@cat file.out
 !,
               '', "a\nb");
@@ -219,4 +219,14 @@ run_make_test('$(file <)', '',
 run_make_test('$(file foo)', '',
               "#MAKEFILE#:1: *** file: invalid file operation: foo.  Stop.\n", 512);
 
+# SV 17448: check whitespace
+create_file('out1', "1\n");
+
+run_make_test(q!
+all:;$(info $(file <  out1  ))
+!,
+              '', "1\n#MAKE#: 'all' is up to date.");
+
+unlink('out1');
+
 1;