Update libtool to 2.4.7

The libtool 1.5.26 is bundled with PHP since the very early days of the
Autotools build system to ease the building process and avoid additional
dependency on the system Libtool.

This updates the bundled libtool to the current 2.4.7 version.

Fixes:

- Fixed race conditions when building PHP in parallel ("cannot create
  .libs" warnings).

Steps done:

```
git clone https://git.savannah.gnu.org/git/libtool.git
cd libtool
git checkout v2.4.7
./bootstrap
cp build-aux/ltmain.sh \
  m4/libtool.m4 \
  m4/lt\~obsolete.m4 \
  m4/ltoptions.m4 \
  m4/ltsugar.m4 \
  m4/ltversion.m4 \
  ../php-src/build/
```

Author: petk

CONTRIBUTING.md

@@ -171,8 +171,7 @@ locations.
     ├─ ax_*.m4                      # https://github.com/autoconf-archive/autoconf-archive
     ├─ config.guess                 # https://git.savannah.gnu.org/cgit/config.git
     ├─ config.sub                   # https://git.savannah.gnu.org/cgit/config.git
-    ├─ libtool.m4                   # https://git.savannah.gnu.org/cgit/libtool.git
-    ├─ ltmain.sh                    # https://git.savannah.gnu.org/cgit/libtool.git
+    ├─ libtool.m4, lt*              # https://git.savannah.gnu.org/cgit/libtool.git
     ├─ pkg.m4                       # https://gitlab.freedesktop.org/pkg-config/pkg-config
     ├─ shtool                       # https://www.gnu.org/software/shtool/
     └─ ...

Zend/Zend.m4

@@ -135,7 +135,7 @@ dnl Ugly hack to check if dlsym() requires a leading underscore in symbol name.
 dnl
 AC_DEFUN([LIBZEND_DLSYM_CHECK],[
 AC_MSG_CHECKING([whether dlsym() requires a leading underscore in symbol names])
-_LT_AC_TRY_DLOPEN_SELF([
+_LT_TRY_DLOPEN_SELF([
   AC_MSG_RESULT(no)
 ], [
   AC_MSG_RESULT(yes)