classes/waf: Fix builds when B != S

Waf requires that the current working directory be ${S} (the location of
the wscript) when building. Most of the time, this was true only because
B defaults to S. However, anything that changed that behavior (notably,
using externalsrc) would break the recipe. Remedy this by explicitly
changing cwd to ${S} when running waf commands. As a happy side effect,
B can be set up for "out of tree" builds to keep the source directory
clean.

(From OE-Core rev: 62dffb71ce22222c635bd90eaa47dd01f70f9c0f)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/waf.bbclass

@@ -1,6 +1,8 @@
 # avoids build breaks when using no-static-libs.inc
 DISABLE_STATIC = ""
 
+B = "${WORKDIR}/build"
+
 EXTRA_OECONF_append = " ${PACKAGECONFIG_CONFARGS}"
 
 python waf_preconfigure() {
@@ -22,16 +24,16 @@ python waf_preconfigure() {
 do_configure[prefuncs] += "waf_preconfigure"
 
 waf_do_configure() {
-	${S}/waf configure --prefix=${prefix} ${WAF_EXTRA_CONF} ${EXTRA_OECONF}
+	(cd ${S} && ./waf configure -o ${B} --prefix=${prefix} ${WAF_EXTRA_CONF} ${EXTRA_OECONF})
 }
 
 do_compile[progress] = "outof:^\[\s*(\d+)/\s*(\d+)\]\s+"
 waf_do_compile()  {
-	${S}/waf build ${@oe.utils.parallel_make_argument(d, '-j%d', limit=64)}
+	(cd ${S} && ./waf build ${@oe.utils.parallel_make_argument(d, '-j%d', limit=64)})
 }
 
 waf_do_install() {
-	${S}/waf install --destdir=${D}
+	(cd ${S} && ./waf install --destdir=${D})
 }
 
 EXPORT_FUNCTIONS do_configure do_compile do_install