target/mips: Rewrite UHI errno_mips() using switch statement

target/mips: Rewrite UHI errno_mips() using switch statement

Linking on Haiku OS fails:

  /boot/system/develop/tools/bin/../lib/gcc/x86_64-unknown-haiku/8.3.0/../../../../x86_64-unknown-haiku/bin/ld:
  error: libqemu-mips-softmmu.fa.p/target_mips_tcg_sysemu_mips-semi.c.o(.rodata) is too large (0xffff405a bytes)
  /boot/system/develop/tools/bin/../lib/gcc/x86_64-unknown-haiku/8.3.0/../../../../x86_64-unknown-haiku/bin/ld:
  final link failed: memory exhausted
  collect2: error: ld returned 1 exit status

This is because the host_to_mips_errno[] uses errno as index,
for example:

  static const uint16_t host_to_mips_errno[] = {
      [ENAMETOOLONG] = 91,
      ...

and Haiku defines [*] ENAMETOOLONG as:

   12 /* Error baselines */
   13 #define B_GENERAL_ERROR_BASE              INT_MIN
   ..
   22 #define B_STORAGE_ERROR_BASE              (B_GENERAL_ERROR_BASE + 0x6000)
  ...
  106 #define B_NAME_TOO_LONG                   (B_STORAGE_ERROR_BASE + 4)
  ...
  211 #define ENAMETOOLONG                      B_TO_POSIX_ERROR(B_NAME_TOO_LONG)

so the array ends up beeing indeed too big.

Since POSIX errno can't be use as indexes on Haiku,
rewrite errno_mips() using a switch statement.

[*] https://github.com/haiku/haiku/blob/r1beta3/headers/os/support/Errors.h#L130

Reported-by: Richard Zak <richard.j.zak@gmail.com>
Suggested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210706130723.1178961-1-f4bug@amsat.org>