The $Id$ keywords were used in Subversion where they can be substituted
with filename, last revision number change, last changed date, and last
user who changed it.

In Git this functionality is different and can be done with Git attribute
ident. These need to be defined manually for each file in the
.gitattributes file and are afterwards replaced with 40-character
hexadecimal blob object name which is based only on the particular file
contents.

This patch simplifies handling of $Id$ keywords by removing them since
they are not used anymore.

Commit 0782a7fc6314c8bd3cbfd57f12d0479bf9cc8dc7 ("Fixed bug #74866
extension_dir = "./ext" now use current directory for base") modified
the php_load_zend_extension_cb() function to use php_load_shlib(), and
pass a handle to the newly introduced zend_load_extension_handle()
function instead of passing the extension path to
zend_load_extension().

While doing so, it introduced a call to php_load_shlib() from code
that is built even when HAVE_LIBDL is not defined. However,
php_load_shlib() is not implemented when HAVE_LIBDL is not defined,
for obvious reasons.

It turns out that zend_load_extension_handle() anyway doesn't do
anything when ZEND_EXTENSIONS_SUPPORT is defined to 0, and
ZEND_EXTENSIONS_SUPPORT is not defined when HAVE_LIBDL is not defined
(Zend/zend_portability.h).

Fixes the following build failure when building on a system that
doesn't have libdl:

main/php_ini.o: In function `php_load_zend_extension_cb':
php_ini.c:(.text+0x478): undefined reference to `php_load_shlib'
php_ini.c:(.text+0x4b0): undefined reference to `php_load_shlib'
collect2: error: ld returned 1 exit status

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Minimize the #ifdef surface area
Localize orig_libpath to retry scope
Send errors to php_error() rathern than stderr

Allow extension name as INI 'extension=' and dl() argument
No BC break, as file name is still accepted.
When using the '-z' command line option (CLI/CGI), an absolute file name must still be provided (nothing changed here)
Change comments in example INI files