Revert "[variable-search] Remove unused imports."

This reverts commit 79a81b14fea3b15003958bf1ad644f459052916a.
Bug 7458: Implement calls to math library functions

* sources/dfmc/llvm-back-end/llvm-primitives-float.dylan
  ($libm-attribute-list): New constant.
  (op--call-libm): New utility emitter for generating calls to C library
   <math.h> functions.
  (primitive primitive-single-float-tan,
   primitive primitive-single-float-asin,
   primitive primitive-single-float-acos,
   primitive primitive-single-float-atan,
   primitive primitive-double-float-tan,
   primitive primitive-double-float-asin,
   primitive primitive-double-float-acos,
   primitive primitive-double-float-atan): Implement by generating calls
   to corresponding C library transcendental functions.
Bug 7458: Fix primitive-copy-vector

* sources/dfmc/llvm-back-end/llvm-primitives-basic.dylan
  (primitive primitive-copy-vector): Fix an error which caused the
   original vector to be returned rather than the newly allocated
   copy.
Bug 7458: Fix primitive-set-generic-function-entrypoints

* sources/dfmc/llvm-back-end/llvm-primitives-lambda.dylan
  (primitive-set-generic-function-entrypoints): Fix the count used with
   the gf-optional-xep entry point.
Bug 7458: Allow default sections in emit-definition-section

* sources/dfmc/llvm-linker/llvm-link-object.dylan
  (emit-definition-section): Allow returning #f as the section to use
   for storing object definitions.
Bug 7458: Use default sections on Mac OS X for now

* sources/dfmc/llvm-back-end/llvm-sections.dylan
  (llvm-section-name): Store all data in the default section for now,
   since the Boehm-Demers-Weiser isn't looking for these sections to
   register them as roots.
Bug 7458: Fix primitive-apply

* sources/dfmc/llvm-back-end/llvm-primitives-lambda.dylan
  (primitive primitive-apply): Handle the arguments vector properly;
   its final element contains a vector of arguments to be appended
   after the other elements.
Bug 7458: Fix more primitive-function type errors in runtime code

* sources/common-dylan/byte-vector.dylan
  (byte-storage-address): Cast a <raw-pointer> to <raw-address>
   before storing in a <machine-word>.

* sources/common-dylan/darwin-common-extensions.dylan
  (darwin-sysctl): Ensure integer-as-raw is called on a value that is
   known to be an <integer>. Use the proper raw type for passing a
   NULL pointer.

* sources/common-dylan/unix-common-extensions.dylan
  (write-console): Ensure integer-as-raw is called on a value that is
   known to be an <integer>.