Add workaround for buggy gcc warnings in our Ruby 2.7 image

Fixes these bogus warnings (that get turned into errors in our CI):

```
../../../../ext/datadog_profiling_native_extension/collectors_stack.c: In function ‘sample_thread’:
../../../../ext/datadog_profiling_native_extension/collectors_stack.c:303:7: error: missing initializer for field ‘build_id_id’ of ‘struct ddog_prof_Mapping’ [-Werror=missing-field-initializers]
  303 |       .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
      |       ^
In file included from /usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/profiling.h:13,
                 from ../../../../ext/datadog_profiling_native_extension/libdatadog_helpers.h:3,
                 from ../../../../ext/datadog_profiling_native_extension/collectors_stack.c:5:
/usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/common.h:520:36: note: ‘build_id_id’ declared here
  520 |   struct ddog_prof_ManagedStringId build_id_id;
      |                                    ^~~~~~~~~~~
../../../../ext/datadog_profiling_native_extension/collectors_stack.c: In function ‘maybe_add_placeholder_frames_omitted’:
../../../../ext/datadog_profiling_native_extension/collectors_stack.c:382:5: error: missing initializer for field ‘build_id_id’ of ‘struct ddog_prof_Mapping’ [-Werror=missing-field-initializers]
  382 |     .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
      |     ^
In file included from /usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/profiling.h:13,
                 from ../../../../ext/datadog_profiling_native_extension/libdatadog_helpers.h:3,
                 from ../../../../ext/datadog_profiling_native_extension/collectors_stack.c:5:
/usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/common.h:520:36: note: ‘build_id_id’ declared here
  520 |   struct ddog_prof_ManagedStringId build_id_id;
      |                                    ^~~~~~~~~~~
../../../../ext/datadog_profiling_native_extension/collectors_stack.c: In function ‘record_placeholder_stack’:
../../../../ext/datadog_profiling_native_extension/collectors_stack.c:429:5: error: missing initializer for field ‘build_id_id’ of ‘struct ddog_prof_Mapping’ [-Werror=missing-field-initializers]
  429 |     .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
      |     ^
In file included from /usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/profiling.h:13,
                 from ../../../../ext/datadog_profiling_native_extension/libdatadog_helpers.h:3,
                 from ../../../../ext/datadog_profiling_native_extension/collectors_stack.c:5:
/usr/local/bundle/gems/libdatadog-16.0.1.1.0-x86_64-linux/vendor/libdatadog-16.0.1/x86_64-linux/libdatadog-x86_64-unknown-linux-gnu/lib/pkgconfig/../../include/datadog/common.h:520:36: note: ‘build_id_id’ declared here
  520 |   struct ddog_prof_ManagedStringId build_id_id;
      |                                    ^~~~~~~~~~~
cc1: all warnings being treated as errors
```

ext/datadog_profiling_native_extension/collectors_stack.c

@@ -300,7 +300,7 @@ void sample_thread(
     }
 
     buffer->locations[i] = (ddog_prof_Location) {
-      .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
+      .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C(""), .build_id_id = {}},
       .function = (ddog_prof_Function) {.name = name_slice, .filename = filename_slice},
       .line = line,
     };
@@ -379,7 +379,7 @@ static void maybe_add_placeholder_frames_omitted(VALUE thread, sampling_buffer*
   ddog_CharSlice function_name = DDOG_CHARSLICE_C("");
   ddog_CharSlice function_filename = {.ptr = frames_omitted_message, .len = strlen(frames_omitted_message)};
   buffer->locations[buffer->max_frames - 1] = (ddog_prof_Location) {
-    .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
+    .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C(""), .build_id_id = {}},
     .function = (ddog_prof_Function) {.name = function_name, .filename = function_filename},
     .line = 0,
   };
@@ -426,7 +426,7 @@ void record_placeholder_stack(
   ddog_CharSlice placeholder_stack
 ) {
   ddog_prof_Location placeholder_location = {
-    .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
+    .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C(""), .build_id_id = {}},
     .function = {.name = DDOG_CHARSLICE_C(""), .filename = placeholder_stack},
     .line = 0,
   };

ext/datadog_profiling_native_extension/heap_recorder.c

@@ -678,7 +678,7 @@ static int st_object_records_iterate(DDTRACE_UNUSED st_data_t key, st_data_t val
   for (uint16_t i = 0; i < stack->frames_len; i++) {
     const heap_frame *frame = &stack->frames[i];
     locations[i] = (ddog_prof_Location) {
-      .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C("")},
+      .mapping = {.filename = DDOG_CHARSLICE_C(""), .build_id = DDOG_CHARSLICE_C(""), .build_id_id = {}},
       .function = {
         .name = {.ptr = frame->name, .len = strlen(frame->name)},
         .filename = {.ptr = frame->filename, .len = strlen(frame->filename)},