Add Options for Variation in C Runtime

[RealTrippR]

Currently, Odin only gives 1 option to link against the C runtime: -no-crt or crt. By default, Odin links against the static C runtime, which is suitable for the majority of use cases, but introduces complications when linking Odin code against code compiled for use with a dynamically linked C runtime.
(See the example at the bottom)

---

The addition of a `-crt-mode` compiler flag could address this issue.

  -crt-mode:<string>
                Specificies the C Run Time to be linked.
                Default: static
                Choices:
                        none
                        static
                        dynamic
                        release-static
                        release-dynamic
                        debug-static
                        debug-dynamic

none - equivalent to -no-crt
static - links to a statically linked CRT, debug-static if the -debug flag is set, otherwise to release-static
dynamic - links to a dynamically linked CRT, debug-dynamic if the -debug flag is set, otherwise to release-dynamic
release-static links to a statically linked release CRT, regardless of the -debug flag.
release-dynamic links to a dynamically linked release CRT, regardless of the -debug flag.
debug-static links to a statically linked debug CRT, regardless of the -debug flag.
debug-dynamic links to a dynamically linked debug CRT, regardless of the -debug flag.

---

Example Test:

#include <stdint.h>
#include <ctype.h>

int32_t is_space(char c) {
    return isspace(c);
}

package test
import "core:c"
import "core:fmt"
foreign import ex "is_space.o"
foreign ex {
    @(link_name="is_space")
    isspace :: proc(s: c.char) -> c.int32_t ---
}
main :: proc() {
    fmt.println(isspace(' '))
    fmt.println(isspace('\t'))
    fmt.println(isspace('\a'))
}

is_space.o: is_space.c
	gcc -c -g is_space.c -o ./is_space.o

ctest.exe:  is_space.o ctest.odin
	odin build ./  -out:ctest.exe  -debug

run: ctest.exe
	./ctest.exe

Running make ctest.exe should result in the linker error:
error LNK2019: unresolved external symbol __imp_isspace referenced in function is_space
caused by mismatch in expected CRT types.

---

Implementation

PROPOSAL-PROCESS.md doesn't specify anything about providing an existing implementation of a proposed feature, but if it helps I have a written a working implementation of -crt-mode. It didn't require much change to the existing compiler (around 120 lines were modified).

[laytan]

One thing is that this is really windows specific.

On unix you could benefit from something like this to switch between glibc, musl, cosmic libc, etc. But those actually have different struct layouts and definitions too. At that point it's almost something like a subtarget.