ucontext structure is different between musl and glibc for ppc
therefore its not enough just to check for arch alone, we also
need to check for libc type.

Fixes errors like

Source/JavaScriptCore/heap/MachineStackMarker.cpp:90:65: error: 'struct mcontext_t' has no member named 'uc_regs'; did you mean 'gregs'?
     thread->suspendedMachineContext = *userContext->uc_mcontext.uc_regs;

Upstream-Status: Pending

Signed-off-by: Khem Raj <raj.khem@gmail.com>

Index: webkitgtk-2.16.3/Source/JavaScriptCore/heap/MachineStackMarker.cpp
===================================================================
--- webkitgtk-2.16.3.orig/Source/JavaScriptCore/heap/MachineStackMarker.cpp
+++ webkitgtk-2.16.3/Source/JavaScriptCore/heap/MachineStackMarker.cpp
@@ -88,7 +88,7 @@ static void pthreadSignalHandlerSuspendR
     }
 
     ucontext_t* userContext = static_cast<ucontext_t*>(ucontext);
-#if CPU(PPC)
+#if CPU(PPC) && defined(__GLIBC__)
     threadData->suspendedMachineContext = *userContext->uc_mcontext.uc_regs;
 #else
     threadData->suspendedMachineContext = userContext->uc_mcontext;