Index: llvm/trunk/tools/llvm-config/BuildVariables.inc.in
===================================================================
--- llvm/trunk/tools/llvm-config/BuildVariables.inc.in
+++ llvm/trunk/tools/llvm-config/BuildVariables.inc.in
@@ -26,3 +26,4 @@
 #define LLVM_LIBDIR_SUFFIX "@LLVM_LIBDIR_SUFFIX@"
 #define LLVM_TARGETS_BUILT "@LLVM_TARGETS_BUILT@"
 #define LLVM_SYSTEM_LIBS "@LLVM_SYSTEM_LIBS@"
+#define LLVM_BUILD_SYSTEM "@LLVM_BUILD_SYSTEM@"
Index: llvm/trunk/tools/llvm-config/CMakeLists.txt
===================================================================
--- llvm/trunk/tools/llvm-config/CMakeLists.txt
+++ llvm/trunk/tools/llvm-config/CMakeLists.txt
@@ -24,6 +24,8 @@
 set(LLVM_CPPFLAGS "${CMAKE_CPP_FLAGS} ${CMAKE_CPP_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
 set(LLVM_CFLAGS "${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
 set(LLVM_CXXFLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
+set(LLVM_BUILD_SYSTEM cmake)
+
 # Use the C++ link flags, since they should be a superset of C link flags.
 set(LLVM_LDFLAGS "${CMAKE_CXX_LINK_FLAGS}")
 set(LLVM_BUILDMODE ${CMAKE_BUILD_TYPE})
Index: llvm/trunk/tools/llvm-config/Makefile
===================================================================
--- llvm/trunk/tools/llvm-config/Makefile
+++ llvm/trunk/tools/llvm-config/Makefile
@@ -65,6 +65,8 @@
 	  >> temp.sed
 	$(Verb) $(ECHO) 's/@LLVM_TARGETS_BUILT@/$(subst /,\/,$(TARGETS_TO_BUILD))/' \
 	  >> temp.sed
+	$(Verb) $(ECHO) 's/@LLVM_BUILD_SYSTEM@/autoconf/' \
+	  >> temp.sed
 	$(Verb) $(SED) -f temp.sed < $< > $@
 	$(Verb) $(RM) temp.sed
 
Index: llvm/trunk/tools/llvm-config/llvm-config.cpp
===================================================================
--- llvm/trunk/tools/llvm-config/llvm-config.cpp
+++ llvm/trunk/tools/llvm-config/llvm-config.cpp
@@ -157,6 +157,7 @@
   --host-target     Target triple used to configure LLVM.\n\
   --build-mode      Print build mode of LLVM tree (e.g. Debug or Release).\n\
   --assertion-mode  Print assertion mode of LLVM tree (ON or OFF).\n\
+  --build-system    Print the build system used to build LLVM (autoconf or cmake).\n\
 Typical components:\n\
   all               All LLVM libraries (default).\n\
   engine            Either a native JIT or a bitcode interpreter.\n";
@@ -323,6 +324,8 @@
 #else
         OS << "ON\n";
 #endif
+      } else if (Arg == "--build-system") {
+        OS << LLVM_BUILD_SYSTEM << '\n';
       } else if (Arg == "--obj-root") {
         OS << ActivePrefix << '\n';
       } else if (Arg == "--src-root") {