Export of internal Abseil changes.

--
4e043a11b4c10a24e84046827ee16f47e11e35cc by Abseil Team <absl-team@google.com>:

Merge of https://github.com/abseil/abseil-cpp/pull/136

PiperOrigin-RevId: 218197648

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e61f06e1e601061a443feaa8c5207c52437bd641 by Abseil Team <absl-team@google.com>:

Don't include <iostream> into int128, it's wasteful

Including iostream emits a global constructor for initializing std::cout and
friends, which isn't actually used by this file.

PiperOrigin-RevId: 218156386

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8a6c82396e4c956be7f285328aec131cb4965f16 by Xiaoyi Zhang <zhangxy@google.com>:

Fix MSVC compiler warnings on discarding return values of functions with 'nodiscard'
attribute.

PiperOrigin-RevId: 217883401

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abf3e3a0f22bc4070df9dbc9a4ef4d883ed686bf by Tom Manshreck <shreck@google.com>:

Update public README to add new libraries

PiperOrigin-RevId: 217879399

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43b3b420a4e861711abbfbd497b8f2b3de17ec8c by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 217780963

--
1c8831947ca6a65a63842e6bd5f37a7c102a4e1b by Abseil Team <absl-team@google.com>:

Fix typo in a comment (missing comma in usage example).

PiperOrigin-RevId: 217776645
GitOrigin-RevId: 4e043a11b4c10a24e84046827ee16f47e11e35cc
Change-Id: I8999ae928da7a0030b4ecfd8d13da8522fdd013a

CMake/AbseilHelpers.cmake

@@ -62,7 +62,104 @@ function(absl_library)
   endif()
 endfunction()
 
-
+#
+# CMake function to imitate Bazel's cc_library rule.
+#
+# Parameters:
+# NAME: name of target (see Note)
+# HDRS: List of public header files for the library
+# SRCS: List of source files for the library
+# DEPS: List of other libraries to be linked in to the binary targets
+# COPTS: List of private compile options
+# DEFINES: List of public defines
+# LINKOPTS: List of link options
+# PUBLIC: Add this so that this library will be exported under absl:: (see Note).
+# TESTONLY: When added, this target will only be built if user passes -DABSL_RUN_TESTS=ON to CMake.
+#
+# Note:
+#
+# By default, absl_cc_library will always create a library named absl_internal_${NAME},
+# which means other targets can only depend this library as absl_internal_${NAME}, not ${NAME}.
+# This is to reduce namespace pollution.
+#
+# absl_cc_library(
+#   NAME
+#     awesome_lib
+#   HDRS
+#     "a.h"
+#   SRCS
+#     "a.cc"
+# )
+# absl_cc_library(
+#   NAME
+#     fantastic_lib
+#   SRCS
+#     "b.cc"
+#   DEPS
+#     absl_internal_awesome_lib # not "awesome_lib"!
+# )
+#
+# If PUBLIC is set, absl_cc_library will instead create a target named
+# absl_${NAME} and an alias absl::${NAME}.
+#
+# absl_cc_library(
+#   NAME
+#     main_lib
+#   ...
+#   PUBLIC
+# )
+#
+# User can then use the library as absl::main_lib (although absl_main_lib is defined too).
+#
+# TODO: Implement "ALWAYSLINK"
+ function(absl_cc_library)
+  cmake_parse_arguments(ABSL_CC_LIB
+    "DISABLE_INSTALL;PUBLIC;TESTONLY"
+    "NAME"
+    "HDRS;SRCS;COPTS;DEFINES;LINKOPTS;DEPS"
+    ${ARGN}
+  )
+   if (NOT ABSL_CC_LIB_TESTONLY OR ABSL_RUN_TESTS)
+    if (ABSL_CC_LIB_PUBLIC)
+      set(_NAME "absl_${ABSL_CC_LIB_NAME}")
+    else()
+      set(_NAME "absl_internal_${ABSL_CC_LIB_NAME}")
+    endif()
+     # Check if this is a header-only library
+    if ("${ABSL_CC_LIB_SRCS}" STREQUAL "")
+      set(ABSL_CC_LIB_IS_INTERFACE 1)
+    else()
+      set(ABSL_CC_LIB_IS_INTERFACE 0)
+    endif()
+     if(NOT ABSL_CC_LIB_IS_INTERFACE)
+      add_library(${_NAME} STATIC "")
+      target_sources(${_NAME} PRIVATE ${ABSL_CC_LIB_SRCS} ${ABSL_CC_LIB_HDRS})
+      target_include_directories(${_NAME}
+        PUBLIC ${ABSL_COMMON_INCLUDE_DIRS})
+      # TODO(rongjiecomputer): Revisit ABSL_COMPILE_CXXFLAGS when fixing GH#123
+      target_compile_options(${_NAME}
+        PRIVATE ${ABSL_COMPILE_CXXFLAGS} ${ABSL_CC_LIB_COPTS})
+      target_link_libraries(${_NAME}
+        PUBLIC ${ABSL_CC_LIB_DEPS}
+        PRIVATE ${ABSL_CC_LIB_LINKOPTS}
+      )
+      target_compile_definitions(${_NAME} PUBLIC ${ABSL_CC_LIB_DEFINES})
+       # Add all Abseil targets to a a folder in the IDE for organization.
+      set_property(TARGET ${_NAME} PROPERTY FOLDER ${ABSL_IDE_FOLDER})
+    else()
+      # Generating header-only library
+      add_library(${_NAME} INTERFACE)
+      target_include_directories(${_NAME} INTERFACE ${ABSL_COMMON_INCLUDE_DIRS})
+      target_link_libraries(${_NAME}
+        INTERFACE ${ABSL_CC_LIB_DEPS} ${ABSL_CC_LIB_LINKOPTS}
+      )
+      target_compile_definitions(${_NAME} INTERFACE ${ABSL_CC_LIB_DEFINES})
+    endif()
+     if(ABSL_CC_LIB_PUBLIC)
+      add_library(absl::${ABSL_CC_LIB_NAME} ALIAS ${_NAME})
+    endif()
+  endif()
+endfunction()
 
 #
 # header only virtual target creation