Solaris: Add a CMAKE_HOST_SOLARIS variable (#16061)

Help/manual/cmake-variables.7.rst

@@ -175,6 +175,7 @@ Variables that Describe the System
    /variable/CMAKE_CL_64
    /variable/CMAKE_COMPILER_2005
    /variable/CMAKE_HOST_APPLE
+   /variable/CMAKE_HOST_SOLARIS
    /variable/CMAKE_HOST_SYSTEM_NAME
    /variable/CMAKE_HOST_SYSTEM_PROCESSOR
    /variable/CMAKE_HOST_SYSTEM

Help/release/dev/cmake-host-solaris.rst

@@ -0,0 +1,5 @@
+cmake-host-solaris
+------------------
+
+* A new :variable:`CMAKE_HOST_SOLARIS` variable was introduced to
+  indicate when CMake is running on an Oracle Solaris host.

Help/variable/CMAKE_HOST_SOLARIS.rst

@@ -0,0 +1,6 @@
+CMAKE_HOST_SOLARIS
+------------------
+
+``True`` for Oracle Solaris operating systems.
+
+Set to ``true`` when the host system is Oracle Solaris.

Source/cmState.cxx

@@ -1425,6 +1425,9 @@ void cmState::Snapshot::SetDefaultDefinitions()
     this->SetDefinition("APPLE", "1");
     this->SetDefinition("CMAKE_HOST_APPLE", "1");
   #endif
+  #if defined(__sun__)
+    this->SetDefinition("CMAKE_HOST_SOLARIS", "1");
+  #endif
 
     char temp[1024];
     sprintf(temp, "%d", cmVersion::GetMinorVersion());