This commit fixes at least two issues.
* Fix a build with clang on linux
```
/usr/bin/ld: cannot open linker script file nuttx.ld: No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```
* Restore symbol renaming for clang on linux
I guess it actually depends on the linker.
For now, use CONFIG_HOST_MACOS.
This fixed the following crash seen with sim/linux built with clang.
```
#135462 0x0000000000404a81 in nxtask_exithook (tcb=0x48f310 <g_idletcb>, status=1, nonblocking=0 '\000') at task/task_exithook.c:618
#135463 0x0000000000402aed in exit (status=1) at task/exit.c:103
#135464 0x0000000000475833 in host_abort (status=1) at sim/up_hostmisc.c:48
#135465 0x000000000040e6c6 in up_assert (filename=0x47b167 "semaphore/sem_wait.c", lineno=113) at sim/up_assert.c:126
#135466 0x000000000040850b in _assert (filename=0x47b167 "semaphore/sem_wait.c", linenum=113) at assert/lib_assert.c:36
#135467 0x0000000000403a40 in nxsem_wait (sem=0x7fca38b1c2d0) at semaphore/sem_wait.c:113
#135468 0x0000000000403b43 in sem_wait (sem=0x7fca38b1c2d0) at semaphore/sem_wait.c:271
#135469 0x000000000040aad3 in lib_stream_semtake (list=0x7fca38b1c2d0) at stdio/lib_libstream.c:159
#135470 0x000000000040a8e7 in lib_flushall (list=0x7fca38b1c2d0) at stdio/lib_libflushall.c:61
#135471 0x0000000000404c3c in nxtask_flushstreams (tcb=0x48f310 <g_idletcb>) at task/task_exithook.c:520
#135472 0x0000000000404a81 in nxtask_exithook (tcb=0x48f310 <g_idletcb>, status=1, nonblocking=0 '\000') at task/task_exithook.c:618
#135473 0x0000000000402aed in exit (status=1) at task/exit.c:103
#135474 0x0000000000475833 in host_abort (status=1) at sim/up_hostmisc.c:48
#135475 0x000000000040e6c6 in up_assert (filename=0x47b167 "semaphore/sem_wait.c", lineno=113) at sim/up_assert.c:126
#135476 0x000000000040850b in _assert (filename=0x47b167 "semaphore/sem_wait.c", linenum=113) at assert/lib_assert.c:36
#135477 0x0000000000403a40 in nxsem_wait (sem=0x7fca38b1c2d0) at semaphore/sem_wait.c:113
#135478 0x0000000000403b43 in sem_wait (sem=0x7fca38b1c2d0) at semaphore/sem_wait.c:271
#135479 0x000000000040aad3 in lib_stream_semtake (list=0x7fca38b1c2d0) at stdio/lib_libstream.c:159
#135480 0x000000000040a8e7 in lib_flushall (list=0x7fca38b1c2d0) at stdio/lib_libflushall.c:61
#135481 0x0000000000404c3c in nxtask_flushstreams (tcb=0x48f310 <g_idletcb>) at task/task_exithook.c:520
```
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