Define -DLLVM_BUILD_TELEMETRY to be used in ifdef (llvm#126746)

Background: 

Telemetry code isn't always built (controlled by this
LLVM_BUILD_TELEMETRY cmake flag)
This means users of the library may not have the library. So we're
definding the `-DLLVM_BUILD_TELEMETRY` to be used in ifdef.

Author: oontvoo

lldb/source/Core/CMakeLists.txt

@@ -18,7 +18,6 @@ endif()
 
 if (LLVM_BUILD_TELEMETRY)
    set(TELEMETRY_DEPS Telemetry)
-   add_definitions(-DLLDB_BUILD_TELEMETRY)
 endif()
 
 # TODO: Add property `NO_PLUGIN_DEPENDENCIES` to lldbCore

lldb/source/Core/Telemetry.cpp

@@ -6,7 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifdef LLDB_BUILD_TELEMETRY
+#include "llvm/Config/llvm-config.h"
+
+#ifdef LLVM_BUILD_TELEMETRY
 
 #include "lldb/Core/Telemetry.h"
 #include "lldb/Core/Debugger.h"
@@ -71,4 +73,4 @@ llvm::Error TelemetryManager::preDispatch(TelemetryInfo *entry) {
 } // namespace telemetry
 } // namespace lldb_private
 
-#endif // LLDB_BUILD_TELEMETRY
+#endif // LLVM_BUILD_TELEMETRY

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -201,4 +201,7 @@
 /* Define if logf128 is available */
 #cmakedefine LLVM_HAS_LOGF128
 
+/* Define if building LLVM with LLVM_BUILD_TELEMETRY */
+#cmakedefine LLVM_BUILD_TELEMETRY ${LLVM_BUILD_TELEMETRY}
+
 #endif