According to my testing the bug is present also on RHEL-6, tested with
rpm-4.8.0-55.el6 and rpm-4.8.0-37.el6.

+++ This bug was initially created as a clone of Bug #1246746 +++

Description of problem:
Recursively and conditionally defined macro behave differently in RHEL-6 (4.8) and RHEL-7 (4.11).
Fedora (version 4.12) behaves like RHEL-6, which seems correct)

Version-Release number of selected component (if applicable):
  rpm-build-4.11.1-25.el7

How reproducible:
  Always

Steps to Reproduce:
  Use in the spec 

  %if "%{?scl}" == "rh-php56"
  %global sub_prefix more-php56-
  %else
  %global sub_prefix %{?scl_prefix}
  %endif

  Name: %{?sub_prefix}php-pecl-%{pecl_name}

During SCL build, and %SCL = "php56"

Actual results:
  RHEL-6 and Fedora 21+
  Name is php56-php-pecl-name (correct)

  RHEL-7
  Name is php-pecl-name  (missing prefix)


Expected results:
  Name always php56-php-pecl-name


Additional info:
Example spec file : https://raw.githubusercontent.com/remicollet/remirepo/master/php/pecl/php-pecl-apfd/php-pecl-apfd.spec

Workaround: less conditionally defined macro (used in previous spec)
  %if 0%{?scl:1}
  %if "%{scl}" == "rh-php56"
  %global sub_prefix more-php56-
  %else
  %global sub_prefix %{scl_prefix}
  %endif
  %endif

Used to build https://www.softwarecollections.org/en/scls/remi/php56more/