Export of internal Abseil changes

--
017c3924d21132085bc20c9be0ae469bfbf2c56c by Gennadiy Rozental <rogeeff@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 338723934

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8b08c23d7b05232e283b1388cee3eb5bebc2d9c4 by Derek Mauro <dmauro@google.com>:

Add script to test GCC floor (the minimum version of GCC we support,
currently the GCC 5 series)

PiperOrigin-RevId: 338708581

--
afa440ac7c843126b4f99b89ebc071dda1d85a4d by Abseil Team <absl-team@google.com>:

Fix typo in documentation of StatusOr::value_or() ('of' -> 'if').

PiperOrigin-RevId: 338690089

--
97d5008865327fc36b942b96de0d0cacfb909df5 by Derek Mauro <dmauro@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 338568224

--
da5e09a7fedb3217329465d9206b7cbc6677176b by Abseil Team <absl-team@google.com>:

Add `absl_btree_prefer_linear_node_search`

Allow keys of `btree_set`, `btree_map`, `btree_multiset`, and `btree_multimap`
to opt-in to linear search (instead of binary search).  Linear search was
used previously for arithmetic types with `key_compare` of `std::greater`
or `std::less`.

For example, this would be useful for key types that wrap an integer
and define their own cheap `operator<()`.

```
 class K {
  public:
   using absl_btree_prefer_linear_node_search = std::true_type;
   ...
  private:
   friend bool operator<(K a, K b) { return a.k_ < b.k_; }
   int k_;
 };

 absl::btree_map<K, V> m;  // Uses linear search
 assert((absl::btree_map<K, V>::testonly_uses_linear_node_search()));
```

PiperOrigin-RevId: 338476553

--
c56ead7ce6b0a5ad32e3a42904c686448a69451e by Gennadiy Rozental <rogeeff@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 338419417
GitOrigin-RevId: 017c3924d21132085bc20c9be0ae469bfbf2c56c
Change-Id: I1199f3ae917280a3ef20ccc6038abbe34d96ec0b

1 files changed, 7 insertions, 11 deletions

diff --git a/absl/time/internal/cctz/include/cctz/civil_time_detail.h b/absl/time/internal/cctz/include/cctz/civil_time_detail.h
index d1b4222b..8aadde57 100644
--- a/absl/time/internal/cctz/include/cctz/civil_time_detail.h
+++ b/absl/time/internal/cctz/include/cctz/civil_time_detail.h
@@ -416,16 +416,10 @@ class civil_time {
 
   // Assigning arithmetic.
   CONSTEXPR_M civil_time& operator+=(diff_t n) noexcept {
-    f_ = step(T{}, f_, n);
-    return *this;
+    return *this = *this + n;
   }
   CONSTEXPR_M civil_time& operator-=(diff_t n) noexcept {
-    if (n != (std::numeric_limits<diff_t>::min)()) {
-      f_ = step(T{}, f_, -n);
-    } else {
-      f_ = step(T{}, step(T{}, f_, -(n + 1)), 1);
-    }
-    return *this;
+    return *this = *this - n;
   }
   CONSTEXPR_M civil_time& operator++() noexcept { return *this += 1; }
   CONSTEXPR_M civil_time operator++(int) noexcept {
@@ -442,13 +436,15 @@ class civil_time {
 
   // Binary arithmetic operators.
   friend CONSTEXPR_F civil_time operator+(civil_time a, diff_t n) noexcept {
-    return a += n;
+    return civil_time(step(T{}, a.f_, n));
   }
   friend CONSTEXPR_F civil_time operator+(diff_t n, civil_time a) noexcept {
-    return a += n;
+    return a + n;
   }
   friend CONSTEXPR_F civil_time operator-(civil_time a, diff_t n) noexcept {
-    return a -= n;
+    return n != (std::numeric_limits<diff_t>::min)()
+               ? civil_time(step(T{}, a.f_, -n))
+               : civil_time(step(T{}, step(T{}, a.f_, -(n + 1)), 1));
   }
   friend CONSTEXPR_F diff_t operator-(civil_time lhs, civil_time rhs) noexcept {
     return difference(T{}, lhs.f_, rhs.f_);