checks for already built extremely expensive builds

ShellB3/shallbethree.sh

@@ -1727,6 +1727,7 @@ mk_ply() { #this is part of pycparser as pycparser.ply, but that is its own util
 }
 
 mk_llvm() {
+  _find_cots MYSELF include/llvm/Config/llvm-config.h $BASE && return 0
   export REQUIRES_RTTI=1  # see https://github.com/llvmpy/llvmpy/issues/29
   name=llvm
   tarball=src/optional/llvm-${LLVMVER}.src.tar.gz
@@ -1946,6 +1947,7 @@ SOSAYWEALL
 }
 
 mk_boost() {
+  _find_cots MYSELF include/boost/any.hpp $BASE && return 0
   name=boost 
   tarball=src/experimental/boost_${BOOSTVER}.tar.bz2
   buildir=boost_${BOOSTVER}