Put bcache inside "namespace gdb"

This avoids a conflict with a system "struct bcache" on
Solaris (see e.g.
https://www.isi.edu/nsnam/archive/ns-users/webarch/2001/msg05393.html)

Note that the Solaris conflict for now only surfaces with
--enable-targets=all (which the build bot doesn't use).

gdb/ChangeLog:

2019-12-06  Christian Biesinger  <cbiesinger@google.com>

	* bcache.c: Put in namespace gdb.
	* bcache.h: Likewise.
	* gdbtypes.c (check_types_worklist): Update.
	(types_deeply_equal): Update.
	* macrotab.c (struct macro_table) <bcache>: Update.
	(new_macro_table): Update.
	* macrotab.h (struct bcache): Put this forward declaration
	inside namespace gdb.
	(new_macro_table): Update.
	* objfiles.h (struct objfile_per_bfd_storage) <filename_cache>:
	Update.
	<macro_cache>: Update.
	* psymtab.h: (psymtab_storage) <psymbol_cache>: Update.

Change-Id: I843d5e91f7ccb3db6d1099a8214c15a74510256f

gdb/bcache.c

@@ -25,6 +25,8 @@
 
 #include <algorithm>
 
+namespace gdb {
+
 /* The type used to hold a single bcache string.  The user data is
    stored in d.data.  Since it can be any type, it needs to have the
    same alignment as the most strict alignment of any type on the host
@@ -378,3 +380,5 @@ bcache::memory_used ()
     return 0;
   return obstack_memory_used (&m_cache);
 }
+
+} /* namespace gdb */