Attempt to address build failures on non-release architectures

• Avoid usage of PATH_MAX not available on hurd

• Enable backtrace generation

  Currently building on hppa fails with:

  test-backtrace.c:10: Assert failed: backtrace_append(bt) == 0
  test-backtrace.c:14: Assert failed: strstr(str_c(bt), "test_backtrace") != NULL
  backtrace_append ..................................................... : FAILED
  test-backtrace.c:34: Assert failed: backtrace_get(&bt) == 0

  on riscv64:

  Debug: backtrace: './test-lib(+0x734d8) [0x2aaab1d4d8]'
  test-backtrace.c:21: Assert failed: strstr(str_c(bt), "test_backtrace_append") != NULL || strstr(str_c(bt), "main") != NULL
  backtrace_append ..................................................... : FAILED
  Debug: backtrace: './test-lib(+0x734d8) [0x2aaab1d4d8]'
  test-backtrace.c:45: Assert failed: strstr(bt, "test_backtrace_get") != NULL || strstr(bt, "main") != NULL
  backtrace_get ........................................................ : FAILED

  on sparc64:

  Debug: backtrace: './test-lib(+0x95ec8) [0x10000095ec8]'
  test-backtrace.c:21: Assert failed: strstr(str_c(bt), "test_backtrace_append") != NULL || strstr(str_c(bt), "main") != NULL
  backtrace_append ..................................................... : FAILED
  Debug: backtrace: './test-lib(+0x95ec8) [0x10000095ec8]'
  test-backtrace.c:45: Assert failed: strstr(bt, "test_backtrace_get") != NULL || strstr(bt, "main") != NULL
  backtrace_get ........................................................ : FAILED