Report system tracing setup failures.

SysTraceStart previously reported success even when no perf events
could be opened, leaving a worker thread running over no buffers
and an empty CPU section without explanation; it now fails in that
case. Also log when /proc/kallsyms cannot be read, which otherwise
silently results in ??? kernel stack frames.

public/client/TracyCallstack.cpp

@@ -1167,7 +1167,11 @@ size_t s_kernelSymCnt;
 static void InitKernelSymbols()
 {
     FILE* f = fopen( "/proc/kallsyms", "rb" );
-    if( !f ) return;
+    if( !f )
+    {
+        TracyDebug( "Failed to read /proc/kallsyms, kernel symbols will be unavailable." );
+        return;
+    }
     tracy::FastVector<KernelSymbol> tmpSym( 512 * 1024 );
     size_t linelen = 16 * 1024;     // linelen must be big enough to prevent reallocs in getline()
     auto linebuf = (char*)tracy_malloc( linelen );

public/client/TracySysTrace.cpp

@@ -1112,6 +1112,14 @@ bool SysTraceStart( int64_t& samplingPeriod )
 
     tracy_free( iter );
 
+    if( s_numBuffers == 0 )
+    {
+        tracy_free( s_ring );
+        s_ring = nullptr;
+        TracyDebug( "Failed to setup any system tracing events, system tracing disabled." );
+        return false;
+    }
+
     traceActive.store( true, std::memory_order_relaxed );
     return true;
 }