Index: llvm/trunk/CMakeLists.txt
===================================================================
--- llvm/trunk/CMakeLists.txt
+++ llvm/trunk/CMakeLists.txt
@@ -833,6 +833,11 @@
           add_definitions("-D_LARGE_FILE_API")
 endif()
 
+# Build with _FILE_OFFSET_BITS=64 on Solaris to match g++ >= 9.
+if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
+          add_definitions("-D_FILE_OFFSET_BITS=64")
+endif()
+
 # Work around a broken bfd ld behavior. When linking a binary with a
 # foo.so library, it will try to find any library that foo.so uses and
 # check its symbols. This is wasteful (the check was done when foo.so
Index: llvm/trunk/cmake/config-ix.cmake
===================================================================
--- llvm/trunk/cmake/config-ix.cmake
+++ llvm/trunk/cmake/config-ix.cmake
@@ -30,6 +30,12 @@
           list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_LARGE_FILE_API")
 endif()
 
+# Do checks with _FILE_OFFSET_BITS=64 on Solaris, because we will build
+# with those too.
+if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
+          list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_FILE_OFFSET_BITS=64")
+endif()
+
 # include checks
 check_include_file(dlfcn.h HAVE_DLFCN_H)
 check_include_file(errno.h HAVE_ERRNO_H)