Compiling php3 with the following options:
cc -O3 -ma -qstrict
fails in  functions/imap.c
a possible solution is the following patch:

*** functions/imap.c    Mon Feb 14 14:11:46 2000
--- functions/imap.c    Wed Mar  1 13:44:59 2000
***************
*** 2615,2620 ****
--- 2615,2621 ----
                        case ST_DECODE0:
                                state++;
                        case ST_NORMAL:
+                               break;
                        }
                }
        }
***************
*** 2671,2676 ****
--- 2672,2678 ----
                                *outp++ |= UNB64(*inp);
                                state = ST_DECODE0;
                        case ST_NORMAL:
+                               break;
                        }
                }
        }
***************
*** 2797,2802 ****
--- 2799,2805 ----
                                *outp++ = B64(*inp++);
                                state = ST_ENCODE0;
                        case ST_NORMAL:
+                               break;
                        }
                }
        }