Building ARM code on OS X - ios

Question

I am targeting the Cortex-A7 (ARMv7-A)
As a test:
bootstrap.s
.globl _start
_start:
mov sp,#0x00010000
bl main
hang: b hang
main.c
int main(void) { return 0; }
Trying:
$ as -arch armv7 -march=armv7-a -mcpu=cortex-a7 -mfloat-abi=hard -mfpu=neon-vfpv4 bootstrap.s -o bootstrap.o
$ file bootstrap.o
bootstrap.o: Mach-O object arm
$ clang -c -arch armv7 -march=armv7-a -mcpu=cortex-a7 -mfloat-abi=hard -mfpu=neon-vfpv4 main.c -o main.o
$ file main.o
notmain.o: Mach-O object arm
Confirms the compilation of Mach-O arm object files (also verified using hexdump, otool, gobjdump)
But now we try to link them together:
$ ld -e _start -arch armv7 bootstrap.o main.o -o foo
ld: warning: -ios_version_min not specified, assuming 6.0
ld: building for iOS, but linking in object file built for OSX, file 'bootstrap.o' for architecture armv7
And we have some issues. Not sure what's going on here. I haven't asked to link-in any iOS-related stuff. Using the -t linker flag confirms that no other objects are being linked in. Not sure why it thinks bootstrap.o is built for OS X when it clearly is a Mach-O arm file. Not sure if I'm passing the right flags to the assembler (pretty much all of them are undocumented?) or the linker
Note that this is for a bare-metal mini-project running on RPi2. I'm going to gobjcopy the linked executable object to a flat binary anyways. I'm just working with Mach-O since that's the only object type the system linker on OS X is capable of working with (and fat Mach-O). If I built a separate cross-compiler, I would be doing the exact same thing, instead I'd be linking ELF files before converting them to flat binary (I can output ELF32 files using clang/llvm anyways, I just cant link them). Seems silly to build a separate cross-compiler when clang/llvm is a perfectly suitable cross-compiler that's able to target my microarchitecture