core: Unbreak build on FreeBSD (#8762)

* CrashReporter: restore explicit environ(7) after 8bbeee1173

BSD systems don't declare environ(7) in any header like POSIX suggests.

src/signal-safe.cpp:12:23: error: use of undeclared identifier 'environ'
   12 |     for (char** var = environ; *var != nullptr; var++) {
      |                       ^

* fix

---------

Co-authored-by: Vaxry <vaxry@vaxry.net>

src/signal-safe.cpp

@@ -7,6 +7,10 @@
 #include <unistd.h>
 #include <cstring>
 
+// NOLINTNEXTLINE
+extern "C" char** environ;
+
+//
 char const* sigGetenv(char const* name) {
     const size_t len = strlen(name);
     for (char** var = environ; *var != nullptr; var++) {