[DynInst_API:] [dyninst/dyninst] c73726: Fix dyninstAPI_RT files to build with older glibc ...

[kupsch <noreply@xxxxxxxxxx>]

  Branch: refs/heads/master
  Home:   https://github.com/dyninst/dyninst
  Commit: c7372633a036c91f731098e538609e55866e6cf8
      https://github.com/dyninst/dyninst/commit/c7372633a036c91f731098e538609e55866e6cf8
  Author: kupsch <kupsch@xxxxxxxxxxx>
  Date:   2022-04-08 (Fri, 08 Apr 2022)

  Changed paths:
    M dyninstAPI_RT/src/RTheap-linux.c
    M dyninstAPI_RT/src/RTheap.c
    M dyninstAPI_RT/src/RTlinux.c
    M dyninstAPI_RT/src/RTposix.c
    M dyninstAPI_RT/src/RTsignal.c

  Log Message:
  -----------
  Fix dyninstAPI_RT files to build with older glibc (#1252)

Replace feature test macro _DEFAULT_SOURCE with _GNU_SOURCE to support older version of glibc