Enable building IPC components on Cygwin.

Reportedly, Boost.Interprocess has been fixed on Cygwin, so we can enable
building IPC components by default on this target.

Refs https://github.com/boostorg/interprocess/issues/242.

CMakeLists.txt

@@ -310,8 +310,6 @@ else()
 endif()
 
 if (CYGWIN)
-    # Boost.Interprocess does not compile on Cygwin: https://github.com/boostorg/interprocess/issues/242
-    set(BOOST_LOG_WITHOUT_IPC ON)
     list(APPEND boost_log_common_private_defines
         __USE_W32_SOCKETS
         _XOPEN_SOURCE=600

build/Jamfile.v2

@@ -179,8 +179,6 @@ project
         <target-os>windows:<library>advapi32
 
         <target-os>cygwin:<define>BOOST_USE_WINDOWS_H
-        # Boost.Interprocess does not compile on Cygwin: https://github.com/boostorg/interprocess/issues/242
-        <target-os>cygwin:<define>BOOST_LOG_WITHOUT_IPC
         <target-os>cygwin:<library>ws2_32
         <target-os>cygwin:<library>mswsock
         <target-os>cygwin:<library>advapi32

doc/changelog.qbk

@@ -9,6 +9,10 @@
 
 [section:changelog Changelog]
 
+[heading 2.34, Boost 1.91]
+
+* Enabled building interprocess communication support on Cygwin by default.
+
 [heading 2.33, Boost 1.90]
 
 * Fixed a missed optimization in `value_ref` visitation.