Bug 7458: Normalize constant <values> rest as part of fixed

* sources/dfmc/llvm-back-end/llvm-emit-computation.dylan
  (emit-computation on <values>): Add values from a constant reference
   rest-value to the fixed values.
Bug 7458: Constant versions of tagging routines

* sources/dfmc/llvm-back-end/llvm-ops.dylan
  (op--tag-integer on <abstract-integer>): New method to construct a constant
   tagged representation of an <integer>.
  (op--tag-character on <llvm-value>): New method to tag a value as a character.
  (op--tag-character on <character>): New method to construct a constant
   tagged representation of a <character>.

* sources/dfmc/llvm-back-end/llvm-emit-object.dylan
  (emit-object on <abstract-integer>): Define using op--tag-integer.
  (emit-object on <character>): Define using op--tag-character.
Bug 7458: Fix generation of defined-constant references

* sources/dfmc/llvm-back-end/llvm-emit-computation.dylan
  (emit-reference on <defined-constant-reference>): Load the constant
   value from the constant definition global, declaring the value as
   invarant to allow eliminating subsequent loads.
dylan: Re-order initializations

* sources/dylan/dylan.lid
  (array, multidimensional-array, limited-array): Re-order to appear
   after the initialization of limited vectors so that
   $empty-dimensions can reference the empty limited integer vector
   instance.
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.
dfmc-modeling: Export more compile-time raw types

* sources/dfmc/modeling/modeling-library.dylan
  (module dfmc-modeling): Export <&raw-c-signed-int> and <&raw-c-pointer>.
Bug 7458: Properly emit null pointer literals

* sources/dfmc/llvm-back-end/llvm-emit-object.dylan
  (emit-object): Add a new method so that literals of type
   <&raw-pointer>, <&raw-c-pointer>, or <&raw-byte-string>
   can be output as LLVM null constants.
Bug 7458: Fix generation of closure reference value transfers

* sources/dfmc/llvm-back-end/llvm-emit-computation.dylan
  (emit-transfer): Generate closure references when the source
   temporary is in an enclosing function environment.
Bug 7458: Fix primitive-byte-allocate-leaf-filled-terminated

* sources/dfmc/llvm-back-end/llvm-primitives-alloc.dylan
  (primitive primitive-byte-allocate-leaf-filled-terminated): Fix
   rounding up the allocation size to the next machine word.
Bug 7458: Fix op--mv-extract-rest

* sources/dfmc/llvm-back-end/llvm-mv.dylan
  (op--mv-extract-rest): Fix an invalid memory access beyond the end
   of the target <simple-object-vector>.
[build-system] Remove unused variables.
[docs] Document the <C-size-t> work.
Merge pull request #830 from waywardmonkeys/add-size-t-docs

[docs] Document the <C-size-t> work.
Merge pull request #832 from waywardmonkeys/remove-build-system-variables

[build-system] Remove unused variables.
[configure] Check more directories for libgc.

Use a list and a for loop to find the gc library file. We now
also check in /usr/lib64 and /usr/local/lib64 by default.

If there are 32 bit systems that also have a lib64, there might
be issues with this if there is a /usr/lib64/libgc.* but we wanted
to find /usr/local/lib/libgc.* instead. I'm not sure that this
would be an issue in actual practice.

Fixes #833.
[configure] Don't always look for GC_LIBRARY.

We only need GC_LIBRARY set when we are using GC_USE_STATIC_BOEHM,
which is only the case by default on Mac OS X, which means that we
don't need to go through all of this logic on other platforms.
[configure] Reset some values when using MPS.

When using MPS, make sure that GC_LFLAGS, GC_LIBRARY and
GC_USE_STATIC_BOEHM are reset to the correct values.
[configure] Check that the -lgc is valid.

Also, only add ${with_gc_path} to CFLAGS / LFLAGS when it is set.
[configure] Don't always search default directories.

When searching for a static libgc, only look in the default directories
when --with-gc-path has not been given.
Merge pull request #834 from waywardmonkeys/configure-check-lib64

[configure] Check more directories for libgc.