Explicit check for requires_* rpm defines

Due to different distros and/or versions of rpm mishandling the shorthand
syntax simply use the longer version which get interpreted correctly.

spl-modules.spec.in

@@ -3,9 +3,17 @@
 # require_kver, require_kdir, require_obj constants for us, but if it does not
 # not we attempt to determine the correct values based on your distro.
 
-%{?require_kver: %define kver %{require_kver}}
-%{?require_kdir: %define kdir %{require_kdir}}
-%{?require_kobj: %define kobj %{require_kobj}}
+%if %{defined require_kver}
+%define kver %{require_kver}
+%endif
+
+%if %{defined require_kdir}
+%define kdir %{require_kdir}
+%endif
+
+%if %{defined require_kobj}
+%define kobj %{require_kobj}
+%endif
 
 # kdir:    Full path to the kernel source headers
 # kobj:    Full path to the kernel build objects