Fixup a reference to detail/FunctionalExcept.cpp

Summary: I missed this reference when I moved it to the portability folder. It is already being compiled at its new location.

Reviewed By: yfeldblum

Differential Revision: D3754227

fbshipit-source-id: 357b0c26ddbcefdc7640f6a334150abba90ed711

folly/Makefile.am

@@ -497,10 +497,6 @@ if !HAVE_WEAK_SYMBOLS
 libfollybase_la_SOURCES += detail/MallocImpl.cpp
 endif
 
-if !HAVE_BITS_FUNCTEXCEPT_H
-libfollybase_la_SOURCES += detail/FunctionalExcept.cpp
-endif
-
 if HAVE_BOOST_CONTEXT
 nobase_follyinclude_HEADERS += \
 	fibers/AddTasks.h \