Add check for isblank and a replacement macro if it doesn't exist.

aclocal.m4

@@ -250,6 +250,24 @@ else
 fi
 ])
 
+dnl
+dnl check for isblank(3)
+dnl
+AC_DEFUN(SUDO_FUNC_ISBLANK,
+[AC_MSG_CHECKING(for isblank)
+AC_CACHE_VAL(sudo_cv_func_isblank,
+[rm -f conftestdata; > conftestdata
+AC_TRY_RUN([#include <ctype.h>
+main() { (void)isblank(1); exit(0); }
+], sudo_cv_func_isblank=yes, sudo_cv_func_isblank=no,
+  sudo_cv_func_isblank=no)
+rm -f core core.* *.core])dnl
+AC_MSG_RESULT($sudo_cv_func_isblank)
+if test $sudo_cv_func_isblank = yes; then
+  AC_DEFINE(HAVE_ISBLANK)
+fi
+])
+
 dnl
 dnl check for sa_len field in struct sockaddr
 dnl

config.h.in

@@ -125,6 +125,12 @@
 /* Define if you want to use execv() instead of execvp().  */
 #undef USE_EXECV
 
+/* Define if you have isblank(3).  */
+#undef HAVE_ISBLANK
+#ifndef HAVE_ISBLANK
+#  define isblank(_x)	((_x) == ' ' || (_x) == '\t')
+#endif
+
 /* Define if you have tzset(3).  */
 #undef HAVE_TZSET
 

configure.in

@@ -1570,6 +1570,7 @@ AC_CHECK_FUNCS(innetgr _innetgr, AC_CHECK_FUNCS(getdomainname) [break])
 AC_CHECK_FUNCS(lsearch, , [AC_CHECK_LIB(compat, lsearch, AC_CHECK_HEADER(search.h, AC_DEFINE(HAVE_LSEARCH) [LIBS="${LIBS} -lcompat"], AC_LIBOBJ(lsearch)), AC_LIBOBJ(lsearch))])
 AC_CHECK_FUNCS(utime, SUDO_FUNC_UTIME_POSIX, AC_LIBOBJ(utime))
 SUDO_FUNC_FNMATCH(AC_DEFINE(HAVE_FNMATCH), AC_LIBOBJ(fnmatch))
+SUDO_FUNC_ISBLANK
 AC_REPLACE_FUNCS(strerror strcasecmp sigaction)
 AC_CHECK_FUNCS(snprintf vsnprintf asprintf vasprintf, , [NEED_SNPRINTF=1])
 dnl