There is no walkcontext(3) for musl libc, so we effectively
disable backtracing symbols without removing the functions.
They just always return zero symbols.

--- src/mongo/platform/backtrace.cpp	2015-08-24 02:39:52.000000000 +0200
+++ src/mongo/platform/backtrace.cpp	2015-08-26 19:27:26.738866698 +0200
@@ -81,7 +81,7 @@
 // to Linux's display, but slightly different.
 //
 int addrtosymstr(void* address, char* outputBuffer, int outputBufferSize) {
-    Dl_info_t symbolInfo;
+    Dl_info symbolInfo;
     if (dladdr(address, &symbolInfo) == 0) {  // no info: "[address]"
         return snprintf(outputBuffer, outputBufferSize, "[0x%p]", address);
     }
@@ -113,10 +113,15 @@
+#if defined(__sunos__)
     if (getcontext(&context) != 0) {
         return 0;
     }
     int wcReturn = walkcontext(
         &context,
         reinterpret_cast<WalkcontextCallbackFunc>(WalkcontextCallback::callbackFunction),
         static_cast<void*>(&walkcontextCallback));
+#else
+    // We have no walkcontext(3) for musl libc
+    int wcReturn = -1;
+#endif
     if (wcReturn == 0) {
         return walkcontextCallback.getCount();
     }