tests: misc: skip a test if the absolute top build dir is unsafe

Without this change, this test would fail during 'make distcheck', for
example.

* tests/misc/exec-bad-unicode.sh: Skip the test if $abs_top_builddir has
spaces or special characters.
* cfg.mk (_tb_misc): Also match tests/misc/exec-bad-unicode.sh.
Reported by Bruno Haible.

cfg.mk

@@ -988,7 +988,7 @@ exclude_file_name_regexp--sc_prohibit_continued_string_alpha_in_column_1 = \
   ^src/(system\.h|od\.c|printf\.c|getlimits\.c)$$
 
 _cksum = ^tests/cksum/cksum-base64\.pl$$
-_tb_misc = misc/(stdbuf|responsive)
+_tb_misc = misc/(exec-bad-unicode|stdbuf|responsive)
 exclude_file_name_regexp--sc_prohibit_test_backticks = \
   ^tests/(local\.mk|(init|$(_tb_misc)|factor/create-test)\.sh)$$|$(_cksum)
 

tests/misc/exec-bad-unicode.sh

@@ -19,6 +19,15 @@
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 
+# stdbuf fails when the absolute top build dir name contains e.g.,
+# space, TAB, NL
+lf='
+'
+case $abs_top_builddir in
+  *[\\\"\#\$\&\'\`$lf\ \	]*)
+    skip_ "unsafe absolute build directory name: $abs_top_builddir";;
+esac
+
 script="$(bad_unicode)"
 
 # Create a program with invalid Unicode in its name.