Do not embed rpath to external libraries

Some distributions, like Debian, generally do not permit rpath to be
set. Add a configure option that disables rpath inclusion to external
libraries.

Change-Id: Ieb1b16d3a154fdf9da09902dc8a27dd1be0a530e
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/clangcodemodel/clangcodemodel.pro

@@ -9,7 +9,9 @@ DEFINES += CLANGCODEMODEL_LIBRARY
 DEFINES += CLANG_VERSION=\\\"$${LLVM_VERSION}\\\"
 DEFINES += "\"CLANG_RESOURCE_DIR=\\\"$${LLVM_LIBDIR}/clang/$${LLVM_VERSION}/include\\\"\""
 
-unix:QMAKE_LFLAGS += -Wl,-rpath,\'$$LLVM_LIBDIR\'
+unix {
+    !disable_external_rpath: QMAKE_LFLAGS += -Wl,-rpath,\'$$LLVM_LIBDIR\'
+}
 
 SOURCES += \
     activationsequencecontextprocessor.cpp \

src/tools/clangbackend/clangbackend.pro

@@ -16,5 +16,5 @@ SOURCES += clangbackendmain.cpp
 
 unix {
     !osx: QMAKE_LFLAGS += -Wl,-z,origin
-    QMAKE_LFLAGS += -Wl,-rpath,$$shell_quote($${LLVM_LIBDIR})
+    !disable_external_rpath: QMAKE_LFLAGS += -Wl,-rpath,$$shell_quote($${LLVM_LIBDIR})
 }