Improve crash backtrace reliability

We're now able to pretty print a C++ backtrace upon crashing in pretty
much any runtime execution scenario. The default pledge sandbox policy
on Linux is now to return EPERM. If you call pledge and have debugging
functions linked (e.g. GetSymbolTable) then the symbol table shall get
loaded before any security policy is put in place. This change updates
build/bootstrap/fixupobj too and fixes some other sneaky build errors.

examples/crashreport2.cc

@@ -7,6 +7,7 @@
 │   • http://creativecommons.org/publicdomain/zero/1.0/            │
 ╚─────────────────────────────────────────────────────────────────*/
 #endif
+#include "libc/calls/calls.h"
 #include "libc/math.h"
 #include "libc/runtime/runtime.h"
 
@@ -18,6 +19,17 @@ void crash(long x0, long x1, long x2,  //
 void (*pCrash)(long, long, long, double, double, double) = crash;
 
 int main(int argc, char *argv[]) {
+
+  // // by default we launch an addr2line subprocess to print backtraces
+  // // with line numbers. you can force it to use the embedded solution
+  // setenv("ADDR2LINE", "", true);
+
+  // // using a seccomp sandbox is another way to force embedded backtraces
+  // pledge("stdio", NULL);
+
+  // enable the crash reporting feature
   ShowCrashReports();
+
+  // time to die
   pCrash(1, 2, 3, NAN, NAN, NAN);
 }