There aren't any configure options in PHP configure which would expect /usr/local/lib as parameter (drop the /lib part from it)

OK, I did.
Same result.

checking for ZLIB support... yes
checking if the location of ZLIB install directory is defined... /usr/local
checking for gzgets in -lz... no
configure: error: ZLIB extension requires zlib >= 1.0.9

Here is a bigger part of config.log in case it gives a better idea of what is going on:

configure:18124: checking for gzgets in -lz
configure:18143: gcc -o conftest -g -O2  -R/usr/local/lib -L/usr/local/lib  -R/usr/local/lib -L/usr/local/lib conftest.c -lz  -lm  -lgssapi -lkrb5 -lasn1 -lcrypto -lroken -lcrypt -lcom_err -lssl -lcrypto 1>&5
/usr/local/lib/libkrb5.so: warning: warning: mktemp() possibly used unsafely; consider using mkstemp()
/usr/lib/libgssapi.so: undefined reference to `krb5_rd_cred2'
/usr/lib/libgssapi.so: undefined reference to `krb5_crypto_destroy'
/usr/lib/libgssapi.so: undefined reference to `krb5_ret_address'
/usr/lib/libgssapi.so: undefined reference to `krb5_ret_data'
/usr/lib/libgssapi.so: undefined reference to `krb5_ret_keyblock'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_setremotesubkey'
/usr/lib/libgssapi.so: undefined reference to `krb5_data_free'
/usr/lib/libgssapi.so: undefined reference to `krb5_config_get_strings'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_setlocalsubkey'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_generatelocalsubkey'
/usr/lib/libgssapi.so: undefined reference to `krb5_sockaddr2address'
/usr/lib/libgssapi.so: undefined reference to `krb5_cc_get_ops'
/usr/lib/libgssapi.so: undefined reference to `krb5_get_default_principal'
/usr/lib/libgssapi.so: undefined reference to `krb5_cc_copy_cache'
/usr/lib/libasn1.so: undefined reference to `init_error_table'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_setkey'
/usr/lib/libgssapi.so: undefined reference to `krb5_get_forwarded_creds'
/usr/lib/libgssapi.so: undefined reference to `krb5_get_err_text'
/usr/lib/libgssapi.so: undefined reference to `krb5_ret_int32'
/usr/lib/libgssapi.so: undefined reference to `krb5_h_addr2sockaddr'
/usr/lib/libgssapi.so: undefined reference to `krb5_build_authenticator'
/usr/lib/libgssapi.so: undefined reference to `krb5_build_ap_req'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_getremoteseqnumber'
/usr/lib/libgssapi.so: undefined reference to `krb5_data_zero'
/usr/lib/libgssapi.so: undefined reference to `krb5_storage_free'
/usr/lib/libgssapi.so: undefined reference to `krb5_config_free_strings'
/usr/lib/libgssapi.so: undefined reference to `krb5_create_checksum'
/usr/lib/libgssapi.so: undefined reference to `krb5_generate_random_block'
/usr/lib/libgssapi.so: undefined reference to `krb5_crypto_init'
/usr/lib/libgssapi.so: undefined reference to `krb5_enctype_to_keytype'
/usr/lib/libgssapi.so: undefined reference to `krb5_free_creds_contents'
/usr/lib/libgssapi.so: undefined reference to `krb5_storage_from_mem'
/usr/lib/libgssapi.so: undefined reference to `krb5_store_address'
/usr/lib/libgssapi.so: undefined reference to `krb5_decrypt_ivec'
/usr/lib/libasn1.so: undefined reference to `initialize_error_table_r'
/usr/lib/libgssapi.so: undefined reference to `krb5_store_int16'
/usr/lib/libgssapi.so: undefined reference to `krb5_ret_int16'
/usr/lib/libgssapi.so: undefined reference to `krb5_get_error_string'
/usr/lib/libgssapi.so: undefined reference to `krb5_principal_match'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_setlocalseqnumber'
/usr/lib/libgssapi.so: undefined reference to `krb5_storage_to_data'
/usr/lib/libgssapi.so: undefined reference to `krb5_store_int32'
/usr/lib/libgssapi.so: undefined reference to `krb5_encrypt_ivec'
/usr/lib/libgssapi.so: undefined reference to `krb5_storage_emem'
/usr/lib/libgssapi.so: undefined reference to `krb5_store_data'
/usr/lib/libgssapi.so: undefined reference to `krb5_auth_con_setremoteseqnumber'
/usr/lib/libgssapi.so: undefined reference to `krb5_principal_get_realm'
/usr/lib/libgssapi.so: undefined reference to `krb5_set_error_string'
/usr/lib/libgssapi.so: undefined reference to `krb5_make_principal'
/usr/lib/libgssapi.so: undefined reference to `krb5_store_keyblock'
configure: failed program was:
#line 18132 "configure"
#include "confdefs.h"
/* Override any gcc2 internal prototype to avoid an error.  */
/* We use char because int might match the return type of a gcc2
    builtin and then its argument prototype would still apply.  */
char gzgets();

int main() {
gzgets()
; return 0; }

It's still not PHP bug: Your LD_LIBRARY_PATH is obviously missing a path OR "krb5-config --libs gssapi" returns wrong information.

How come 4.3.10 compiles just fine then? You've changed the configure script in the new builds and now it doesn't detect everything anymore. The old configure script still works well with 4.3.11.

The output of the command your recommended to check:
root@evil# krb5-config --libs gssapi
-L/usr/lib -lgssapi -lkrb5 -lasn1 -lcrypto -lroken -lcrypt -lcom_err

root@evil# ldconfig -r

gives me this:
        19:-lz.2 => /lib/libz.so.2
        139:-lz.1 => /usr/local/lib/libz.so.1

and  /usr/local/lib/libz.so.1 goes to libz.so.1.2.2

root@909# pkg-config --list-all
libpcre          libpcre - PCRE - Perl compatible regular expressions C library
freetype2        FreeType 2 - A free, high-quality, and portable font engine.
libclamav        libclamav - A GPL virus scanner
fontconfig       Fontconfig - Font configuration and customization library
openssl          OpenSSL - Secure Sockets Layer and cryptography libraries and tools
libxml-2.0       libXML - libXML library version2.
xcursor          Xcursor - X Cursor library
libpng12         libpng12 - Loads and saves PNG files
zzip-zlib-config zzip-zlib-config - ZLib Config (for ZZipLib)
libxslt          libxslt - XSLT library version 2.
wv-1.0           wvWare - Word Document Filter library and utilities
zzipwrap         zzipwrap - Callback Wrappers for ZZipLib
zziplib          zziplib - ZZipLib - libZ-based ZIP-access Library
libexslt         libexslt - EXSLT Extension library

I've found the source of the problem.

The krb5 port was installed and it was confusing the new PHP configure script.