Fix default sendmail path when not found during build

Closes GH-5548.

Author: Ingramz

acinclude.m4

@@ -2084,7 +2084,7 @@ dnl Search for the sendmail binary
 dnl
 AC_DEFUN([PHP_PROG_SENDMAIL], [
   PHP_ALT_PATH=/usr/bin:/usr/sbin:/usr/etc:/etc:/usr/ucblib:/usr/lib
-  AC_PATH_PROG(PROG_SENDMAIL, sendmail,[], $PATH:$PHP_ALT_PATH)
+  AC_PATH_PROG(PROG_SENDMAIL, sendmail, /usr/sbin/sendmail, $PATH:$PHP_ALT_PATH)
   PHP_SUBST(PROG_SENDMAIL)
 ])
 

main/main.c

@@ -697,10 +697,8 @@ PHP_INI_MH(OnChangeBrowscap);
  /* Windows use the internal mail */
 #if defined(PHP_WIN32)
 # define DEFAULT_SENDMAIL_PATH NULL
-#elif defined(PHP_PROG_SENDMAIL)
-# define DEFAULT_SENDMAIL_PATH PHP_PROG_SENDMAIL " -t -i "
 #else
-# define DEFAULT_SENDMAIL_PATH "/usr/sbin/sendmail -t -i"
+# define DEFAULT_SENDMAIL_PATH PHP_PROG_SENDMAIL " -t -i"
 #endif
 
 /* {{{ PHP_INI