Autotools: Sync CS in bz2 extension (#15163)

- AS_* macros used
- Checking message refactored

Author: petk

ext/bz2/config.m4

@@ -4,23 +4,17 @@ PHP_ARG_WITH([bz2],
     [Include BZip2 support])])
 
 if test "$PHP_BZ2" != "no"; then
-  if test -r $PHP_BZ2/include/bzlib.h; then
-    BZIP_DIR=$PHP_BZ2
-  else
-    AC_MSG_CHECKING([for BZip2 in default path])
+  AS_IF([test -r $PHP_BZ2/include/bzlib.h], [BZIP_DIR=$PHP_BZ2], [
     for i in /usr/local /usr; do
-      if test -r $i/include/bzlib.h; then
-        BZIP_DIR=$i
-        AC_MSG_RESULT([found in $i])
-        break
-      fi
+      AS_IF([test -r $i/include/bzlib.h], [BZIP_DIR=$i; break;])
     done
-  fi
+  ])
 
-  if test -z "$BZIP_DIR"; then
-    AC_MSG_RESULT([not found])
-    AC_MSG_ERROR([Please reinstall the BZip2 distribution])
-  fi
+  AC_MSG_CHECKING([for BZip2])
+  AS_VAR_IF([BZIP_DIR],, [
+    AC_MSG_RESULT([bzlib.h not found])
+    AC_MSG_ERROR([Please reinstall the BZip2 library package])
+  ], [AC_MSG_RESULT([found in $BZIP_DIR])])
 
   PHP_CHECK_LIBRARY([bz2], [BZ2_bzerror], [
     PHP_ADD_INCLUDE([$BZIP_DIR/include])