package/gcc: transition PowerPC 32 to secureplt

package/gcc: transition PowerPC 32 to secureplt

PowerPC has two PLT models: BSS-PLT and Secure-PLT. BSS-PLT uses
runtime code generation to generate the PLT stubs. Secure-PLT was
introduced with GCC 4.1 and Binutils 2.17 (base has GCC 4.2.1 and
Binutils 2.17), and is a more secure PLT format, using a read-only
linkage table, with the dynamic linker populating a non-executable
index table.

References to other distro/BSD transitions:
  https://patchwork.openembedded.org/patch/106621/
  https://reviews.freebsd.org/D20598

Fixes a bug observed when creating SELinux policy where all apps
require execmem because the heap requires execute before this change.

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>