Enable Altivec for single precision

Altivec only works for single precision.

Signed-off-by: Trent Piepho <tpiepho@gmail.com>

fftw.spec

@@ -309,12 +309,12 @@ for ((i=0; i<2; i++)) ; do
 done
 %endif
 
-#%ifarch ppc ppc64
-## Compile support for Altivec instructions
-#for ((i=0; i<2; i++)) ; do
-#    prec_flags[i]+=" --enable-altivec"
-#done
-#%endif
+%ifarch ppc ppc64
+# Compile support for Altivec instructions; only supported for single precision
+for ((i=0; i<1; i++)) ; do
+    prec_flags[i]+=" --enable-altivec"
+done
+%endif
 
 # Loop over precisions
 for ((iprec=0; iprec<%{nprec}; iprec++)) ; do
@@ -530,6 +530,7 @@ done
 - Clean up precision list
 - Fix for OpenMPI build with < 4 processors
 - Fix building with no enabled MPI types
+- Enable single precision Altivec on PPC
 
 * Thu Mar 02 2023 Orion Poplawski <orion@nwra.com> - 3.3.10-5
 - Use make macros