Describe in details what exactly are you doing and how do you compile it.

Reproduce code:
--------------
1. Download http://downloads.php.net/ilia/php-5.1.0RC4.tar.bz2
2. Unpack and remove ext/oci8 directory
3. Download http://pecl.php.net/get/oci8-1.1.1.tgz
4. Place contents of oci8-1.1.1 direcotry in ext/oci8
5. Execute:

make clean
./buildconf --force
./configure --with-oci8=/usr/local/oracle
make &&
make install


Result:
--------

ext/oci8/oci8.o(.text+0xb44): In function `php_oci_descriptor_flush_hash_dtor':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:749: undefined reference to `php_oci_lob_flush'
ext/oci8/oci8.o(.text+0x24d5): In function `php_oci_column_to_zval':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:1479: undefined reference to `php_oci_lob_read'
ext/oci8/oci8.o(.text+0x25f1): In function `php_oci_fetch_row':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:1560: undefined reference to `php_oci_statement_fetch'
ext/oci8/oci8.o(.text+0x2750):/root/work/web/php-5.1.0/ext/oci8/oci8.c:1568: undefined reference to `php_oci_statement_get_column'
ext/oci8/oci8.o(.text+0x9dd): In function `php_oci_statement_list_dtor':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:668: undefined reference to `php_oci_statement_free'
ext/oci8/oci8.o(.text+0x9fd): In function `php_oci_descriptor_list_dtor':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:676: undefined reference to `php_oci_lob_free'
ext/oci8/oci8.o(.text+0xa1d): In function `php_oci_collection_list_dtor':
/root/work/web/php-5.1.0/ext/oci8/oci8.c:684: undefined reference to `php_oci_collection_close'
ext/oci8/oci8.o(.data+0x4): undefined reference to `zif_oci_define_by_name'
ext/oci8/oci8.o(.data+0x18): undefined reference to `zif_oci_bind_by_name'
ext/oci8/oci8.o(.data+0x2c): undefined reference to `zif_oci_field_is_null'
ext/oci8/oci8.o(.data+0x40): undefined reference to `zif_oci_field_name'
[...]
collect2: ld returned 1 exit status
make: *** [sapi/cli/php] Error 1

Please run `ls -l ext/oci8` and `grep -rnH "oci8" Makefile | grep LIBTOOL` and paste the output here.

1. ls -l ext/oci8 BEFORE make/make install:
total 252
-rw-r--r--  1 rura users   134 Sep  9 15:20 CREDITS
-rw-r--r--  1 rura users  2319 Sep  6 21:31 README
-rw-r--r--  1 rura users 11356 Sep  9 15:20 config.m4
-rw-r--r--  1 rura users   685 Sep  9 15:20 config.w32
-rw-r--r--  1 rura users 57033 Sep 22 14:09 oci8.c
-rw-r--r--  1 rura users  5143 Sep 15 19:25 oci8.dsp
-rw-r--r--  1 rura users 22097 Sep  6 23:42 oci8_collection.c
-rw-r--r--  1 rura users 57313 Sep  7 10:58 oci8_interface.c
-rw-r--r--  1 rura users 21308 Sep  6 23:42 oci8_lob.c
-rw-r--r--  1 rura users 32161 Sep 15 10:28 oci8_statement.c
-rw-r--r--  1 rura users  2520 Sep  9 15:20 php_oci8.h
-rw-r--r--  1 rura users 16903 Sep  6 23:44 php_oci8_int.h
drwxr-xr-x  2 root root   3928 Nov 16 23:06 tests

2. ls -l ext/oci8 AFTER make/make install:
total 396
-rw-r--r--  1 rura users    134 Sep  9 15:20 CREDITS
-rw-r--r--  1 rura users   2319 Sep  6 21:31 README
-rw-r--r--  1 rura users  11356 Sep  9 15:20 config.m4
-rw-r--r--  1 rura users    685 Sep  9 15:20 config.w32
-rw-r--r--  1 rura users  57033 Sep 22 14:09 oci8.c
-rw-r--r--  1 rura users   5143 Sep 15 19:25 oci8.dsp
-rw-r--r--  1 root root     302 Nov 16 23:30 oci8.lo
-rw-r--r--  1 root root  139760 Nov 16 23:30 oci8.o
-rw-r--r--  1 rura users  22097 Sep  6 23:42 oci8_collection.c
-rw-r--r--  1 rura users  57313 Sep  7 10:58 oci8_interface.c
-rw-r--r--  1 rura users  21308 Sep  6 23:42 oci8_lob.c
-rw-r--r--  1 rura users  32161 Sep 15 10:28 oci8_statement.c
-rw-r--r--  1 rura users   2520 Sep  9 15:20 php_oci8.h
-rw-r--r--  1 rura users  16903 Sep  6 23:44 php_oci8_int.h
drwxr-xr-x  2 root root    3928 Nov 16 23:06 tests

3. grep -rnH "oci8" Makefile | grep LIBTOOL
Makefile:430:   $(LIBTOOL) --mode=compile $(CC)  -Iext/oci8/ -I/root/work/web/php-5.1.0/ext/oci8/ $(COMMON_FLAGS) $(CFLAGS_CLEAN) $(EXTRA_CFLAGS) -c /root/work/web/php-5.1.0/ext/oci8/oci8.c -o ext/oci8/oci8.lo

You didn't run ./buildconf or it failed.
No bug here.

What autoconf version are you using?

I used autoconf version 2.59 but now downgraded to 2.13. Buildconf gives me this oputput:

./buildconf --force
Forcing buildconf
using default Zend directory
buildconf: checking installation...
buildconf: autoconf version 2.13 (ok)

When I use downgraded autoconf I still cannot compile new oci8 extension with PHP 5.1.0RC4 or snaphsot php5-200511161130. It works fine with PHP 5.0.5 w/ oci8 1.1  and 5.1.0RC4 with oci8 v 1.0.

Remove ./configure before running ./buildconf --force.

It works! 
I tried removing configure and compiling with autoconf 2.59 but downgraded autoconf did the job.

Thanks for help!