[gdb] Fix data race in bcache::insert

Data race between:
...
  Read of size 8 at 0x7bb4000000d0 by thread T4:
    #0 gdb::bcache::insert(void const*, int, bool*) gdb/bcache.c:155
    #1 objfile_per_bfd_storage::intern(char const*) gdb/objfiles.h:250
    #2 objfile::intern(char const*) gdb/objfiles.h:475
    #3 dwarf2_canonicalize_name gdb/dwarf2/read.c:21904
    #4 dwarf2_name gdb/dwarf2/read.c:21999
    #5 read_base_type gdb/dwarf2/read.c:17092
    #6 read_type_die_1 gdb/dwarf2/read.c:21529
    #7 read_type_die gdb/dwarf2/read.c:21464
    #8 process_die gdb/dwarf2/read.c:8674
    #9 read_file_scope gdb/dwarf2/read.c:9610
    #10 process_die gdb/dwarf2/read.c:8614
    #11 process_full_comp_unit gdb/dwarf2/read.c:8383
    #12 process_queue_item gdb/dwarf2/read.c:7592
...
and:
...
  Previous write of size 8 at 0x7bb4000000d0 by main thread:
    #0 gdb::bcache::insert(void const*, int, bool*) gdb/bcache.c:167
    #1 objfile_per_bfd_storage::intern(std::__cxx11::basic_string<char,
    std::char_traits<char>, std::allocator<char> > const&) gdb/objfiles.h:257
    #2 objfile::intern(std::__cxx11::basic_string<char,
    std::char_traits<char>, std::allocator<char> > const&) <null>
    #3 dwarf2_compute_name gdb/dwarf2/read.c:9050
    #4 dwarf2_full_name gdb/dwarf2/read.c:9070
    #5 read_structure_type gdb/dwarf2/read.c:14558
    #6 process_structure_scope gdb/dwarf2/read.c:14847
    #7 process_die gdb/dwarf2/read.c:8643
    #8 read_file_scope gdb/dwarf2/read.c:9610
    #9 process_die gdb/dwarf2/read.c:8614
    #10 process_full_comp_unit gdb/dwarf2/read.c:8383
    #11 process_queue_item gdb/dwarf2/read.c:7592
...

0 files changed, 0 insertions, 0 deletions