Limit make_jobs for boost < 1.59 (#4984)

Earlier versions of boost had a fixed maximum number of jobs.  1.54
was 64, it bumped once or twice afterwards and in 1.59 [this
commit][commit] it became dynamic.

I need 1.54 for as a prereq for bcl2fastq but I can't build 1.54 on my
144 core build box.

This fixes that.

[commit]: 316e26ca71

var/spack/repos/builtin/packages/boost/package.py

@@ -341,7 +341,11 @@ def install(self, spec, prefix):
         b2name = './b2' if spec.satisfies('@1.47:') else './bjam'
 
         b2 = Executable(b2name)
-        b2_options = ['-j', '%s' % make_jobs]
+        jobs = make_jobs
+        # in 1.59 max jobs became dynamic
+        if jobs > 64 and spec.satisfies('@:1.58'):
+            jobs = 64
+        b2_options = ['-j', '%s' % jobs]
 
         threadingOpts = self.determine_b2_options(spec, b2_options)