Abort from configure when which command is missing (PR#18510).

git-svn-id: https://svn.r-project.org/R/trunk@84286 00db46b3-68df-0310-9c12-caf00c1e9a41

configure

@@ -5433,6 +5433,10 @@ fi
 done
 test -n "$WHICH" || WHICH="which"
 
+if test "${WHICH}" = which ; then
+  as_fn_error $? "which is required but missing" "$LINENO" 5
+fi
+
 ## Make
 : ${MAKE=make}
 
@@ -27054,7 +27058,7 @@ _ACEOF
 # flags.
 r_save_CFLAGS=$CFLAGS
 CFLAGS="$CFLAGS $r_verb"
-(eval echo $as_me:27059: \"$ac_link\") >&5
+(eval echo $as_me:27063: \"$ac_link\") >&5
 r_c_v_output=`eval $ac_link 5>&1 2>&1 | grep -v 'Driving:'`
 echo "$r_c_v_output" >&5
 CFLAGS=$r_save_CFLAGS
@@ -27130,7 +27134,7 @@ _ACEOF
 # flags.
 r_save_CFLAGS=$CFLAGS
 CFLAGS="$CFLAGS $r_cv_prog_c_v"
-(eval echo $as_me:27135: \"$ac_link\") >&5
+(eval echo $as_me:27139: \"$ac_link\") >&5
 r_c_v_output=`eval $ac_link 5>&1 2>&1 | grep -v 'Driving:'`
 echo "$r_c_v_output" >&5
 CFLAGS=$r_save_CFLAGS

configure.ac

@@ -680,6 +680,12 @@ AC_PATH_PROGS(SED, sed, /bin/sed, [/usr/xpg4/bin:$PATH])
 ## 'which' is not POSIX, and might be a shell builtin or alias
 ##  (but should not be in 'sh')
 AC_PATH_PROGS(WHICH, which, which)
+if test "${WHICH}" = which ; then
+  ## needed to build and run R
+  ## ends up hard-coded in the utils package
+  AC_MSG_ERROR([[which is required but missing]])
+fi
+
 ## Make
 : ${MAKE=make}
 AC_SUBST(MAKE)