Fix more -Wundef, in darwin context

src/libutil/current-process.cc

@@ -13,7 +13,7 @@
 # include <mach-o/dyld.h>
 #endif
 
-#if __linux__
+#ifdef __linux__
 # include <mutex>
 # include "nix/util/cgroup.hh"
 # include "nix/util/namespaces.hh"
@@ -23,7 +23,7 @@ namespace nix {
 
 unsigned int getMaxCPU()
 {
-    #if __linux__
+    #ifdef __linux__
     try {
         auto cgroupFS = getCgroupFS();
         if (!cgroupFS) return 0;
@@ -82,7 +82,7 @@ void restoreProcessContext(bool restoreMounts)
     unix::restoreSignals();
     #endif
     if (restoreMounts) {
-        #if __linux__
+        #ifdef __linux__
         restoreMountNamespace();
         #endif
     }
@@ -106,7 +106,7 @@ std::optional<Path> getSelfExe()
 {
     static auto cached = []() -> std::optional<Path>
     {
-        #if __linux__ || __GNU__
+        #if defined(__linux__) || defined(__GNU__)
         return readLink("/proc/self/exe");
         #elif __APPLE__
         char buf[1024];

src/libutil/file-descriptor.cc

@@ -113,7 +113,7 @@ void AutoCloseFD::fsync() const
 
 void AutoCloseFD::startFsync() const
 {
-#if __linux__
+#ifdef __linux__
         if (fd != -1) {
             /* Ignore failure, since fsync must be run later anyway. This is just a performance optimization. */
             ::sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WRITE);

src/libutil/unix/file-descriptor.cc

@@ -163,7 +163,7 @@ void Pipe::create()
 
 //////////////////////////////////////////////////////////////////////
 
-#if __linux__ || __FreeBSD__
+#if defined(__linux__) || defined(__FreeBSD__)
 static int unix_close_range(unsigned int first, unsigned int last, int flags)
 {
 #if !HAVE_CLOSE_RANGE
@@ -179,7 +179,7 @@ void unix::closeExtraFDs()
     constexpr int MAX_KEPT_FD = 2;
     static_assert(std::max({STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO}) == MAX_KEPT_FD);
 
-#if __linux__ || __FreeBSD__
+#if defined(__linux__) || defined(__FreeBSD__)
     // first try to close_range everything we don't care about. if this
     // returns an error with these parameters we're running on a kernel
     // that does not implement close_range (i.e. pre 5.9) and fall back
@@ -189,7 +189,7 @@ void unix::closeExtraFDs()
     }
 #endif
 
-#if __linux__
+#ifdef __linux__
     try {
         for (auto & s : std::filesystem::directory_iterator{"/proc/self/fd"}) {
             checkInterrupt();

src/libutil/unix/processes.cc

@@ -190,7 +190,7 @@ static pid_t doFork(bool allowVfork, ChildWrapperFunction & fun)
 }
 
 
-#if __linux__
+#ifdef __linux__
 static int childEntry(void * arg)
 {
     auto & fun = *reinterpret_cast<ChildWrapperFunction*>(arg);
@@ -213,7 +213,7 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
             logger = makeSimpleLogger();
         }
         try {
-#if __linux__
+#ifdef __linux__
             if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1)
                 throw SysError("setting death signal");
 #endif

src/libutil/unix/signals.cc

@@ -105,7 +105,7 @@ void unix::setChildSignalMask(sigset_t * sigs)
 {
     assert(sigs); // C style function, but think of sigs as a reference
 
-#if _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
+#if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 1) || (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE) || (defined(_POSIX_SOURCE) && _POSIX_SOURCE)
     sigemptyset(&savedSignalMask);
     // There's no "assign" or "copy" function, so we rely on (math) idempotence
     // of the or operator: a or a = a.