Author: Dustin Polke <DuPol@gmx.de>

Header files are located in top_srcdir not top_builddir.
--- a/swig/Makefile.am
+++ b/swig/Makefile.am
@@ -3,7 +3,7 @@ EXTRA_DIST = $(SWIG_SRC) nlopt-guile.i n
 
 BUILT_SOURCES = nlopt-guile.cpp nlopt-python.cpp nlopt-enum-renames.i nlopt.scm.in
 
-HDR = $(top_builddir)/api/nlopt.hpp
+HDR = $(top_srcdir)/api/nlopt.hpp
 
 ##############################################################################
 # Guile wrapper
@@ -11,7 +11,7 @@ HDR = $(top_builddir)/api/nlopt.hpp
 libnlopt@NLOPT_SUFFIX@_guile_la_SOURCES = nlopt-guile.cpp
 libnlopt@NLOPT_SUFFIX@_guile_la_LIBADD = ../libnlopt@NLOPT_SUFFIX@.la
 libnlopt@NLOPT_SUFFIX@_guile_la_LDFLAGS = -version-info @SHARED_VERSION_INFO@
-libnlopt@NLOPT_SUFFIX@_guile_la_CPPFLAGS = $(GUILE_CPPFLAGS) -I$(top_builddir)/api
+libnlopt@NLOPT_SUFFIX@_guile_la_CPPFLAGS = $(GUILE_CPPFLAGS) -I$(top_srcdir)/api
 
 guiledir = $(GUILE_INSTALL_DIR)
 if WITH_GUILE
@@ -25,7 +25,7 @@ endif
 _nlopt_la_SOURCES = nlopt-python.cpp
 _nlopt_la_LIBADD = ../libnlopt@NLOPT_SUFFIX@.la
 _nlopt_la_LDFLAGS = -module -version-info @SHARED_VERSION_INFO@
-_nlopt_la_CPPFLAGS = $(PYTHON_INCLUDES) -I$(top_builddir)/api
+_nlopt_la_CPPFLAGS = $(PYTHON_INCLUDES) -I$(top_srcdir)/api
 
 if WITH_PYTHON
 python_PYTHON = nlopt.py
@@ -43,12 +43,12 @@ lib_LTLIBRARIES = $(guilelib)
 if MAINTAINER_MODE
 
 nlopt-guile.cpp nlopt.scm.in: $(SWIG_SRC) nlopt-guile.i $(HDR)
-	swig -I$(top_builddir)/api -outdir $(builddir) -c++ -guile -scmstub -o $@ nlopt.i
+	swig -I$(top_srcdir)/api -outdir $(builddir) -c++ -guile -scmstub -o $@ nlopt.i
 	rm -f nlopt.scm.in
 	mv nlopt.scm nlopt.scm.in
 
 nlopt-python.cpp nlopt.py: $(SWIG_SRC) nlopt-python.i numpy.i $(HDR)
-	swig -I$(top_builddir)/api -outdir $(builddir) -c++ -python -o $@ nlopt.i
+	swig -I$(top_srcdir)/api -outdir $(builddir) -c++ -python -o $@ nlopt.i
 
 nlopt-enum-renames.i: $(top_srcdir)/api/nlopt.h
 	(echo "// AUTOMATICALLY GENERATED -- DO NOT EDIT"; egrep 'NLOPT_[LG][DN]|NLOPT_AUGLAG|NLOPT_G_MLSL|NLOPT_NUM_ALGORITHMS' $(top_srcdir)/api/nlopt.h | sed 's/NLOPT_//g' |tr -d ' ' |tr '/' ',' |tr '=' ',' |cut -d, -f1 |while read name; do echo "%rename(NLOPT_$$name) nlopt::$$name;"; done; egrep 'NLOPT_[A-Z_]* =' $(top_srcdir)/api/nlopt.h | egrep -v 'NLOPT_[LG][DN]|NLOPT_AUGLAG|NLOPT_G_MLSL' | sed 's/NLOPT_//g' |tr -d ' ' |cut -d'=' -f1 | while read name; do echo "%rename(NLOPT_$$name) nlopt::$$name;"; done) > $@