src: add SafeGetenv() to internal API

Allow it to be used anywhere in src/ that env variables with security
implications are accessed.

PR-URL: nodejs#11006
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/node.cc

@@ -943,7 +943,7 @@ Local<Value> UVException(Isolate* isolate,
 
 
 // Look up environment variable unless running as setuid root.
-inline bool SafeGetenv(const char* key, std::string* text) {
+bool SafeGetenv(const char* key, std::string* text) {
 #ifndef _WIN32
   // TODO(bnoordhuis) Should perhaps also check whether getauxval(AT_SECURE)
   // is non-zero on Linux.

src/node_internals.h

@@ -112,6 +112,8 @@ void RegisterSignalHandler(int signal,
                            bool reset_handler = false);
 #endif
 
+bool SafeGetenv(const char* key, std::string* text);
+
 template <typename T, size_t N>
 constexpr size_t arraysize(const T(&)[N]) { return N; }