Add ability to serialize compilation/linking in cc rules

Specifically, both the C/C++ compiler and link rules now recognize the
cc.serialize boolean variable which instructs them to compiler/link
serially with regards to any other recipe.

This is primarily useful when compiling large translation units or linking
large binaries that require so much memory that doing that in parallel with
other compilation/linking jobs is likely to summon the OOM killer. For
example:

obj{memory-hog}: cc.serialize = true

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