boost: Limit PARALLEL_MAKE by -j 64

* greater paralelism isn't supported by bjam and causes segfault or ignoring -j
* PARALLEL_MAKE was enabled for boost in
  http://git.openembedded.org/openembedded-core/commit/?id=9b9cfc1dfe5e3b8f89b7a8508537166d0f23935e

(From OE-Core rev: c212f306934aa1c7c825e3bb060d4799be1efca1)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/boost/boost.inc

@@ -102,8 +102,22 @@ BJAM_TOOLS   = "-sTOOLS=gcc \
 		'--layout=system' \
 		"
 
-#use PARALLEL_MAKE to speed up the build
-BJAM_OPTS    = '${PARALLEL_MAKE} \
+# use PARALLEL_MAKE to speed up the build, but limit it by -j 64, greater paralelism causes bjam to segfault or to ignore -j
+# https://svn.boost.org/trac/boost/ticket/7634
+def get_boost_parallel_make(bb, d):
+    pm = d.getVar('PARALLEL_MAKE', True)
+    if pm:
+        # people are usually using "-jN" or "-j N", but let it work with something else appended to it
+        import re
+        pm_prefix = re.search("\D+", pm)
+        pm_val = re.search("\d+", pm)
+        if pm_prefix is None or pm_val is None:
+            bb.error("Unable to analyse format of PARALLEL_MAKE variable: %s" % pm)
+        pm_nval = min(64, int(pm_val.group(0)))
+        return pm_prefix.group(0) + str(pm_nval) + pm[pm_val.end():]
+
+BOOST_PARALLEL_MAKE = "${@get_boost_parallel_make(bb, d)}"
+BJAM_OPTS    = '${BOOST_PARALLEL_MAKE} \
 		${BJAM_TOOLS} \
 		-sBOOST_BUILD_USER_CONFIG=${S}/tools/build/v2/user-config.jam \
 		--builddir=${S}/${TARGET_SYS} \