Parent-Child discover error in examples/simple when built as release and shared library.

Describe your environment
My system is Ubuntu 18.04.5 LTS. And the compiler is gcc 7.5.0

Steps to reproduce
I am trying to use opentelemetry as a shared library for my project. But I found that when I try to build it as release and shared library, there is some error in Parent-Child discover. The problem can be reproduced by just running the examples/simple/example_simple. Build in Debug(default) in cmake or static library wont show this error.

I use the following code to build.
cmake .. -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON
cmake --build . --target all

What is the expected behavior?
In example/simple the parent_span_id of f1 should be span_id of f2. And parent_span_id of f2 should be span_id of library. But both showing 0000000000000000.

What is the actual behavior?

{
  name          : f1
  trace_id      : cbbb2e3813a548c408de4b484dc723a1
  span_id       : ce90a9eaf3214e19
  tracestate    : 
  parent_span_id: 0000000000000000
  start         : 1634260358826620364
  duration      : 7665
  description   : 
  span kind     : Internal
  status        : Unset
  attributes    : 
  events        : 
  links         : 
  resources     : 
	service.name: unknown_service
	telemetry.sdk.version: 1.0.0
	telemetry.sdk.language: cpp
	telemetry.sdk.name: opentelemetry
  instr-lib     : foo_library
}
{
  name          : f1
  trace_id      : 3dc7f1b4da6e2eedff960b136ab6e305
  span_id       : a145e9e7fca8f666
  tracestate    : 
  parent_span_id: 0000000000000000
  start         : 1634260358826785278
  duration      : 1634
  description   : 
  span kind     : Internal
  status        : Unset
  attributes    : 
  events        : 
  links         : 
  resources     : 
	service.name: unknown_service
	telemetry.sdk.version: 1.0.0
	telemetry.sdk.language: cpp
	telemetry.sdk.name: opentelemetry
  instr-lib     : foo_library
}
{
  name          : f2
  trace_id      : 94d5abc1a0839e21a97ab9bb3564cbea
  span_id       : 8c0d473664eeeb48
  tracestate    : 
  parent_span_id: 0000000000000000
  start         : 1634260358826616048
  duration      : 296248
  description   : 
  span kind     : Internal
  status        : Unset
  attributes    : 
  events        : 
  links         : 
  resources     : 
	service.name: unknown_service
	telemetry.sdk.version: 1.0.0
	telemetry.sdk.language: cpp
	telemetry.sdk.name: opentelemetry
  instr-lib     : foo_library
}
{
  name          : library
  trace_id      : 0f0bc2eebeb389b448502ac1f015ed1e
  span_id       : 72fdbadc8e352b5d
  tracestate    : 
  parent_span_id: 0000000000000000
  start         : 1634260358826597245
  duration      : 460802
  description   : 
  span kind     : Internal
  status        : Unset
  attributes    : 
  events        : 
  links         : 
  resources     : 
	service.name: unknown_service
	telemetry.sdk.version: 1.0.0
	telemetry.sdk.language: cpp
	telemetry.sdk.name: opentelemetry
  instr-lib     : foo_library
}

Also the there is a test failed passing.

/home/xxx/src/opentelemetry-cpp/sdk/test/trace/tracer_test.cc:130: Failure
Value of: span2.at(0)->GetParentSpanId().IsValid()
  Actual: false
Expected: true
/home/xxx/src/opentelemetry-cpp/sdk/test/trace/tracer_test.cc:142: Failure
Expected equality of these values:
  span1.at(0)->GetTraceId()
    Which is: 16-byte object <11-E7 89-39 C6-F1 C7-94 00-2A 0C-55 77-86 CC-F1>
  span2.at(0)->GetTraceId()
    Which is: 16-byte object <7A-F8 0A-45 00-73 E5-4C 09-3E D9-58 8D-D0 60-F3>
/home/chunhao.shen/src/opentelemetry-cpp/sdk/test/trace/tracer_test.cc:143: Failure
Expected equality of these values:
  span2.at(0)->GetParentSpanId()
    Which is: 8-byte object <00-00 00-00 00-00 00-00>
  span1.at(0)->GetSpanId()
    Which is: 8-byte object <4D-6D D3-1B 08-D4 0C-9F>