minor fix in malloc terminology used in docs (JuliaLang#52665)

doc/src/manual/performance-tips.md

@@ -94,8 +94,8 @@ a vector of 64-bit floats so there should be no need to allocate (heap) memory.
 
 We should clarify that what `@time` reports is specifically *heap* allocations, which are typically needed for either
 mutable objects or for creating/growing variable-sized containers (such as `Array` or `Dict`, strings, or "type-unstable"
-objects whose type is only known at runtime). Allocating (or deallocating) such blocks of memory may require an expensive
-system call (e.g. via `malloc` in C), and they must be tracked for garbage collection. In contrast, immutable values like
+objects whose type is only known at runtime). Allocating (or deallocating) such blocks of memory may require an expensive function
+call to libc (e.g. via `malloc` in C), and they must be tracked for garbage collection. In contrast, immutable values like
 numbers (except bignums), tuples, and immutable `struct`s can be stored much more cheaply, e.g. in stack or CPU-register
 memory, so one doesn’t typically worry about the performance cost of "allocating" them.