This file is a little confusing: it provides all of the mallocr logic,
but is compiled multiple times to produce a unique symbol each time.
For example, building mallocr.c with -DDEFINE_FREER produces freer.o
that only defines _free_r(). This is fine for most symbols, but it's
a little confusing when defining mallocr itself -- we produce a file
with the same symbol name, but we still need -DDEFINE_MALLOCR. In
order to move the logic from the build rules to source files, using
mallocr.c both as a multiplexer and for defining a single symbol is a
bit tricky. It's possible (if we add a lot of redundant preprocessor
checks to mallocr.c, or we add complicated build flags just for this
one files), but it's easier if we simply rename this to a dedicated
file. So let's do that.
We do this as a dedicated commit because the next one will create a
new mallocr.c file and git's automatic diff algorithms can handle
trivial renames, but it can't handle renames+creates in the same
commit.
b1b44f777c