Port abseil to GNU/Hurd.hurd

abseil has failed to build on GNU/Hurd for a long time. Now
let's make it work! :)

Note that `__GNU__` is the macro for detecting GNU/Hurd. And
`__MACH__` is also defined there besides on Apple platform.
They are both "mach" but with different implementation and
platform details. Here are the works,

* Mark platform features (not) supported by GNU/Hurd.

  * Supports `mmap` and `write`.

  * Not supports `vdso`. It's specific to Linux.

  * Not supports `ELF_SYMBOLIZE` for now. GNU/Hurd uses ELF as
    the binary format. But symbolizing in abseil relies on
    reading object file path from `/proc/self/task/<pid>/maps`
    (Linux specific) or `/proc/self/maps`. GNU/Hurd does have
    the latter. However, due to its micro-kernel design, it's
    currently unable to get the file path info there.

  * Disable stack consumption measurement. The problem behind
    it is that GNU/Hurd uses a very different way to implement
    signal handling. Due to compiler behavior, it is
    impossible to get a stable, valid and reliable statictic
    data. In my test environment, it's 96 bytes (< 100) for
    current codes.

* GNU/Hurd uses different errno and messages than Linux. So
  related things are adjusted accordingly.

* Fix a misuse of `__MACH__`, which should actually be
  `__APPLE__`.

* Fix a missing including of `signal.h` for using `SIGABRT`.
  Otherwise compilation will fail with undefined symbol error
  on GNU/Hurd.

Signed-off-by: Yuqian Yang <crupest@crupest.life>

1 files changed, 3 insertions, 1 deletions

diff --git a/absl/base/internal/strerror_test.cc b/absl/base/internal/strerror_test.cc
index e32d5b5c..2eccde77 100644
--- a/absl/base/internal/strerror_test.cc
+++ b/absl/base/internal/strerror_test.cc
@@ -39,7 +39,9 @@ TEST(StrErrorTest, ValidErrorCode) {
 TEST(StrErrorTest, InvalidErrorCode) {
   errno = ERANGE;
   EXPECT_THAT(absl::base_internal::StrError(-1),
-              AnyOf(Eq("No error information"), Eq("Unknown error -1")));
+              AnyOf(Eq("No error information"),
+                    Eq("Unknown error -1"),
+                    Eq("Error in unknown error system: FFFFFFFF")));
   EXPECT_THAT(errno, Eq(ERANGE));
 }