Update UPGRADING.INTERNALS re: removed --disable-inline-optimization switch

This build configuration switch was removed in 3a19726.

Author: alexdowad

UPGRADING.INTERNALS

@@ -138,11 +138,18 @@ PHP 8.0 INTERNALS UPGRADE NOTES
 ========================
 
   a. Abstract
-    - Symbol HAVE_HASH_EXT is removed and is no longer defined. It should be
-      considered to have hash extension always available since PHP 7.4.
-    - Symbol HAVE_PCRE is removed and is no longer defined. It should be
-      considered to have pcre extension always available since PHP 7.4.
-    - Symbol HAVE_LOCALE_H has been removed and is no longer defined.
+    1.  Symbol HAVE_HASH_EXT is removed and is no longer defined. It should be
+        considered to have hash extension always available since PHP 7.4.
+
+    2.  Symbol HAVE_PCRE is removed and is no longer defined. It should be
+        considered to have pcre extension always available since PHP 7.4.
+
+    3.  Symbol HAVE_LOCALE_H has been removed and is no longer defined.
+
+    4.  --disable-inline-optimization (which actually disabled all compiler
+        optimizations) has been removed. If you wish to build PHP on a host
+        with extremely constrained memory, and compilation fails with an "out
+        of memory" message, add "-O0" to CFLAGS.
 
   b. Unix build system changes