sys-libs/libunwind: Sync with Gentoo

It's from Gentoo commit 1c50d13aff87891252b0933f47ef9c2a074b338e.

sdk_container/src/third_party/portage-stable/sys-libs/libunwind/files/libunwind-1.7.2-backport-pr521.patch

@@ -1,31 +0,0 @@
-https://bugs.gentoo.org/913817
-https://github.com/libunwind/libunwind/issues/520
-https://github.com/libunwind/libunwind/pull/521
-
-From aaf9909c91f1fa875907df8d437bff689e00172e Mon Sep 17 00:00:00 2001
-From: Stephen Webb <swebb@blackberry.com>
-Date: Fri, 26 May 2023 16:22:08 -0400
-Subject: [PATCH] Fix FTBFS on Linux ppc32
-
-Looks like the Linux ucontext structure has changed for PPC at some
-point. This probably needs some kind of version check, or else ancient
-kernels will need to stick with 1.6 or earlier.
----
- src/ppc32/ucontext_i.h | 4 ++--
- 1 file changed, 2 insertions(+), 2 deletions(-)
-
-diff --git a/src/ppc32/ucontext_i.h b/src/ppc32/ucontext_i.h
-index 64f8ed878..ee93c6979 100644
---- a/src/ppc32/ucontext_i.h
-+++ b/src/ppc32/ucontext_i.h
-@@ -44,8 +44,8 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
- //#define MQ_IDX                36
- #define LINK_IDX        36
- 
--#define _UC_MCONTEXT_GPR(x) ( (void *)&dmy_ctxt.uc_mcontext.gregs[x] - (void *)&dmy_ctxt) )
--#define _UC_MCONTEXT_FPR(x) ( ((void *)&dmy_ctxt.uc_mcontext.fpregs[x] - (void *)&dmy_ctxt) )
-+#define _UC_MCONTEXT_GPR(x) ( ((void *)&dmy_ctxt.uc_mcontext.uc_regs->gregs[x] - (void *)&dmy_ctxt) )
-+#define _UC_MCONTEXT_FPR(x) ( ((void *)&dmy_ctxt.uc_mcontext.uc_regs->fpregs.fpregs[x] - (void *)&dmy_ctxt) )
- 
- /* These are dummy structures used only for obtaining the offsets of the
-    various structure members. */