Apply LTS transformations for 20211102 LTS branch (#1050)

CMake/AbseilHelpers.cmake

diff --git a/CMake/AbseilHelpers.cmake b/CMake/AbseilHelpers.cmake
index 17c4f44..f2ce567 100644
--- a/CMake/AbseilHelpers.cmake
+++ b/CMake/AbseilHelpers.cmake
@@ -278,7 +278,7 @@
     if(ABSL_ENABLE_INSTALL)
       set_target_properties(${_NAME} PROPERTIES
         OUTPUT_NAME "absl_${_NAME}"
-        SOVERSION 0
+        SOVERSION "2111.0.0"
       )
     endif()
   else()

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d59c2ad..750a475 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -50,7 +50,7 @@
 # This must come before the project() and include(CTest) lines.
 OPTION(BUILD_TESTING "Build tests" OFF)
 
-project(absl LANGUAGES CXX)
+project(absl LANGUAGES CXX VERSION 20211102)
 include(CTest)
 
 # Output directory is correct by default for most build setups. However, when
@@ -175,17 +175,7 @@
 add_subdirectory(absl)
 
 if(ABSL_ENABLE_INSTALL)
-  # absl:lts-remove-begin(system installation is supported for LTS releases)
-  # We don't support system-wide installation
-  list(APPEND SYSTEM_INSTALL_DIRS "/usr/local" "/usr" "/opt/" "/opt/local" "c:/Program Files/${PROJECT_NAME}")
-  if(NOT DEFINED CMAKE_INSTALL_PREFIX OR CMAKE_INSTALL_PREFIX IN_LIST SYSTEM_INSTALL_DIRS)
-    message(WARNING "\
-  The default and system-level install directories are unsupported except in LTS \
-  releases of Abseil.  Please set CMAKE_INSTALL_PREFIX to install Abseil in your \
-  source or build tree directly.\
-    ")
-  endif()
-  # absl:lts-remove-end
+  
 
   # install as a subdirectory only
   install(EXPORT ${PROJECT_NAME}Targets

absl/base/config.h

diff --git a/absl/base/config.h b/absl/base/config.h
index d3cad68..585485c 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -92,8 +92,8 @@
 //
 // LTS releases can be obtained from
 // https://github.com/abseil/abseil-cpp/releases.
-#undef ABSL_LTS_RELEASE_VERSION
-#undef ABSL_LTS_RELEASE_PATCH_LEVEL
+#define ABSL_LTS_RELEASE_VERSION 20211102
+#define ABSL_LTS_RELEASE_PATCH_LEVEL 0
 
 // Helper macro to convert a CPP variable to a string literal.
 #define ABSL_INTERNAL_DO_TOKEN_STR(x) #x

absl/base/options.h

diff --git a/absl/base/options.h b/absl/base/options.h
index 230bf1e..56b4e36 100644
--- a/absl/base/options.h
+++ b/absl/base/options.h
@@ -205,8 +205,8 @@
 // be changed to a new, unique identifier name.  In particular "head" is not
 // allowed.
 
-#define ABSL_OPTION_USE_INLINE_NAMESPACE 0
-#define ABSL_OPTION_INLINE_NAMESPACE_NAME head
+#define ABSL_OPTION_USE_INLINE_NAMESPACE 1
+#define ABSL_OPTION_INLINE_NAMESPACE_NAME lts_20211102
 
 // ABSL_OPTION_HARDENED
 //