Cannot find in-tree libiconv.a after reconfigure.

* acinclude.m4 (AM_ICONV): If we find an in-tree libiconv.a
        that we can use, then cache the path to this archive.
        * configure: Regenerate.

gdb/configure

@@ -8328,6 +8328,7 @@ else
     am_cv_func_iconv="no, consider installing GNU libiconv"
     am_cv_lib_iconv=no
     am_cv_use_build_libiconv=no
+    am_cv_build_libiconv_path=
 
     # If libiconv is part of the build tree, then try using it over
     # any system iconv.
@@ -8353,6 +8354,7 @@ iconv_t cd = iconv_open("","");
 _ACEOF
 if ac_fn_c_try_link "$LINENO"; then :
   am_cv_use_build_libiconv=yes
+          am_cv_build_libiconv_path=$lib_dir/libiconv.a
           am_cv_lib_iconv=yes
           am_cv_func_iconv=yes
 fi
@@ -8361,7 +8363,6 @@ rm -f core conftest.err conftest.$ac_objext \
         LIBS="$am_save_LIBS"
         CPPFLAGS="$am_save_CPPFLAGS"
         if test "$am_cv_use_build_libiconv" = "yes"; then
-          BUILD_LIBICONV_LIBDIR=$lib_dir
           break
         fi
       done
@@ -8438,7 +8439,7 @@ $as_echo "$am_cv_func_iconv" >&6; }
     LIBICONV_INCLUDE=
   fi
   if test "$am_cv_use_build_libiconv" = yes; then
-    LIBICONV="$BUILD_LIBICONV_LIBDIR/libiconv.a"
+    LIBICONV="$am_cv_build_libiconv_path"
     LIBICONV_LIBDIR=""
     LIBICONV_INCLUDE="$BUILD_LIBICONV_INCLUDE"
   fi