[libomp] ompd_init(): fix heap-buffer-overflow when constructing libompd.so path

There is no guarantee that the space allocated in `libname`
is enough to accomodate the whole `dl_info.dli_fname`,
because it could e.g. have an suffix  - `.5`,
and that highlights another problem - what it should do about suffxies,
and should it do anything to resolve the symlinks before changing the filename?

```
$ LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/usr/local/lib"  ./src/utilities/rstest/rstest -c /tmp/f49137920.NEF
dl_info.dli_fname "/usr/local/lib/libomp.so.5"
strlen(dl_info.dli_fname) 26
lib_path_length 14
lib_path_length + 12 26
=================================================================
==30949==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60300000002a at pc 0x000000548648 bp 0x7ffdfa0aa780 sp 0x7ffdfa0a9f40
WRITE of size 27 at 0x60300000002a thread T0
    #0 0x548647 in strcpy (/home/lebedevri/rawspeed/build-Clang-SANITIZE/src/utilities/rstest/rstest+0x548647)
    #1 0x7fb9e3e3d234 in ompd_init() /repositories/llvm-project/openmp/runtime/src/ompd-specific.cpp:102:5
    #2 0x7fb9e3dcb446 in __kmp_do_serial_initialize() /repositories/llvm-project/openmp/runtime/src/kmp_runtime.cpp:6742:3
    #3 0x7fb9e3dcb40b in __kmp_get_global_thread_id_reg /repositories/llvm-project/openmp/runtime/src/kmp_runtime.cpp:251:7
    #4 0x59e035 in main /home/lebedevri/rawspeed/build-Clang-SANITIZE/../src/utilities/rstest/rstest.cpp:491
    #5 0x7fb9e3762d09 in __libc_start_main csu/../csu/libc-start.c:308:16
    #6 0x4df449 in _start (/home/lebedevri/rawspeed/build-Clang-SANITIZE/src/utilities/rstest/rstest+0x4df449)

0x60300000002a is located 0 bytes to the right of 26-byte region [0x603000000010,0x60300000002a)
allocated by thread T0 here:
    #0 0x55cc5d in malloc (/home/lebedevri/rawspeed/build-Clang-SANITIZE/src/utilities/rstest/rstest+0x55cc5d)
    #1 0x7fb9e3e3d224 in ompd_init() /repositories/llvm-project/openmp/runtime/src/ompd-specific.cpp:101:17
    #2 0x7fb9e3762d09 in __libc_start_main csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: heap-buffer-overflow (/home/lebedevri/rawspeed/build-Clang-SANITIZE/src/utilities/rstest/rstest+0x548647) in strcpy
Shadow bytes around the buggy address:
  0x0c067fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c067fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c067fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c067fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c067fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c067fff8000: fa fa 00 00 00[02]fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==30949==ABORTING
Aborted
```