Add AbseilCpp project

Include a revert of a commit[1] that bumps the minimum required Virtual
Studio version to 2019. Since we still support vesion 2017.

[1] abseil/abseil-cpp@dc51d35

Closes: wingtk#1174

gvsbuild/patches/abseil-cpp/0001-Revert-Raise-the-MSVC-floor-to-MSVC-2019-16.0-in-acc.patch

@@ -0,0 +1,32 @@
+From 990724b6130411d9e41afe8a90627413c43cee2f Mon Sep 17 00:00:00 2001
+From: Alessandro Bono <[email protected]>
+Date: Wed, 13 Dec 2023 11:26:02 +0100
+Subject: [PATCH] Revert "Raise the MSVC floor to MSVC 2019 (16.0) in
+ accordance with"
+
+This reverts commit dc51d35fe719b3a3c49f895c149b0920a3745cc4.
+---
+ absl/base/policy_checks.h | 6 +++---
+ 1 file changed, 3 insertions(+), 3 deletions(-)
+
+diff --git a/absl/base/policy_checks.h b/absl/base/policy_checks.h
+index 372e848d..b8cd4c94 100644
+--- a/absl/base/policy_checks.h
++++ b/absl/base/policy_checks.h
+@@ -44,10 +44,10 @@
+ // Toolchain Check
+ // -----------------------------------------------------------------------------
+
+-// We support Visual Studio 2019 (MSVC++ 16.0) and later.
++// We support Visual Studio 2017 (MSVC++ 15.0) and later.
+ // This minimum will go up.
+-#if defined(_MSC_VER) && _MSC_VER < 1920 && !defined(__clang__)
+-#error "This package requires Visual Studio 2019 (MSVC++ 16.0) or higher."
++#if defined(_MSC_VER) && _MSC_VER < 1910 && !defined(__clang__)
++#error "This package requires Visual Studio 2017 (MSVC++ 15.0) or higher."
+ #endif
+
+ // We support GCC 7 and later.
+-- 
+2.34.1
+

gvsbuild/projects/__init__.py

@@ -1,5 +1,6 @@
 # flake8: noqa
 
+from gvsbuild.projects.abseil import AbseilCpp
 from gvsbuild.projects.adwaita_icon_theme import AdwaitaIconTheme
 from gvsbuild.projects.atk import Atk
 from gvsbuild.projects.boringssl import BoringSSL

gvsbuild/projects/abseil.py

@@ -0,0 +1,45 @@
+#  Copyright (C) 2016 The Gvsbuild Authors
+#
+#  This program is free software; you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 2 of the License, or
+#  (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program; if not, see <http://www.gnu.org/licenses/>.
+
+from gvsbuild.utils.base_builders import CmakeProject
+from gvsbuild.utils.base_expanders import Tarball
+from gvsbuild.utils.base_project import Project, project_add
+
+
+@project_add
+class AbseilCpp(Tarball, CmakeProject):
+    def __init__(self):
+        Project.__init__(
+            self,
+            "abseil-cpp",
+            version="20230802.1",
+            archive_url="https://github.com/abseil/abseil-cpp/archive/refs/tags/{version}.tar.gz",
+            hash="987ce98f02eefbaf930d6e38ab16aa05737234d7afbab2d5c4ea7adbe50c28ed",
+            dependencies=[
+                "cmake",
+                "zlib",
+                "ninja",
+            ],
+            patches=[
+                "0001-Revert-Raise-the-MSVC-floor-to-MSVC-2019-16.0-in-acc.patch",
+            ],
+        )
+
+    def build(self):
+        CmakeProject.build(
+            self,
+            cmake_params=r'-DBUILD_SHARED_LIBS=ON -DCMAKE_CXX_STANDARD=14',
+            use_ninja=True,
+        )