RedundantReloadRemover::run: use cached state rather than allocating it new for each function. (#1118)
RedundantReloadRemover::run: use cached state rather than allocating it new for each function. (#1118)

RedundantReloadRemover participates in the state-recycling machinery
implemented in cranelift-codegen/src/context.rs, whose goal it is to cache
per-pass state so it can be used for compilation of multiple functions without
reallocation.  Unfortunately RedundantReloadRemover::run simply ignores the
cached state and reallocates it new for each function.  This patch fixes that.
This reduces the number of malloc'd blocks by about 2%.
stoklund/cretonne,stoklund/cretonne,stoklund/cretonne