Build warning: [-Wpointer-bool-conversion] with LLVM/icx (samples/bluetooth/mesh)

[zephyrbot]

Reported by ashish sinha:

Test case with build warnings raised from LLVM/icx:
samples/bluetooth/mesh

zephyr/subsys/bluetooth/host/mesh/transport.c:982:30: warning: 
      address of 'net_rx->ctx' will always evaluate to 'true'
      [-Wpointer-bool-conversion]
        if (!sdu_len_is_ok(&net_rx->ctx, seg_n)) {
             ~~~~~~~~~~~~~  ~~~~~~~~^~~
1 warning generated.
  CC      subsys/bluetooth/host/mesh/crypto.o
  CC      subsys/bluetooth/host/mesh/access.o
zephyr/subsys/bluetooth/host/mesh/access.c:35:3: warning: 
      duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
} const model_init[] = {
  ^
1 warning generated.
  CC      subsys/bluetooth/host/mesh/cfg.o
  CC      subsys/bluetooth/host/mesh/health.o
  CC      subsys/bluetooth/host/mesh/prov.o
zephyr/subsys/bluetooth/host/mesh/prov.c:616:31: warning: 
      passing 'u8_t [9]' to parameter of type 'const char *' converts between
      pointers to integer types with different sign [-Wpointer-sign]
                        return prov->output_string(str);
                                                   ^~~
zephyr/subsys/bluetooth/host/mesh/prov.c:758:10: warning: 
      passing 'u8_t [16]' to parameter of type 'char *' converts between
      pointers to integer types with different sign [-Wpointer-sign]
        strncpy(link.auth, str, prov->output_size);
                ^~~~~~~~~
zephyr/lib/libc/minimal/include/string.h:20:45: note: 
      passing argument to parameter 'd' here
extern char  *strncpy(char *_MLIBC_RESTRICT d, const char *_MLIBC_RESTRICT s,
                                            ^
2 warnings generated.

how-to-reproduce:

source zephyr-env.sh
export ZEPHYR_GCC_VARIANT=issm
cd samples/bluetooth/mesh
make pristine
make BOARD=quark_se_c1000_devboard CC=icx

(Imported from Jira ZEP-2555)