fftw: fix reconfigure error introduced in previous patch

| config.status: executing libtool commands
| mv: cannot move ‘<WORKDIR>/build’ to ‘<WORKDIR>/build-fftw/build’: Directory not empty
| WARNING: <WORKDIR>/temp/run.do_configure.21632:1 exit 1 from 'mv <WORKDIR>/build <WORKDIR>/build-fftw'
| ERROR: Function failed: do_configure (log file is located at <WORKDIR>/temp/log.do_configure.21632)

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

meta-oe/recipes-support/fftw/fftw_3.3.4.bb

@@ -16,6 +16,7 @@ EXTRA_OECONF = "--disable-fortran --enable-shared --enable-threads"
 
 do_configure() {
     # configure fftw
+    rm -rf ${WORKDIR}/build-fftw
 	mkdir -p ${B}
     cd ${B}
     # full (re)configure
@@ -23,6 +24,7 @@ do_configure() {
     mv ${B} ${WORKDIR}/build-fftw
 
     # configure fftwl
+    rm -rf ${WORKDIR}/build-fftwl
 	mkdir -p ${B}
     cd ${B}
     # configure only
@@ -30,6 +32,7 @@ do_configure() {
     mv ${B} ${WORKDIR}/build-fftwl 
 
     # configure fftwf
+    rm -rf ${WORKDIR}/build-fftwf
 	mkdir -p ${B}
     cd ${B}
     # configure only