src/util: Fix compatibility with glibc 2.33 and higher

From `man 3 errno`: The value in errno is significant only when the
return value of the call indicated an error.

Any code using this failed with: "realpath failed: Invalid argument"

Author: vmihalko

src/util/file_util.cpp

@@ -54,7 +54,7 @@ std::string get_current_working_directory()
   errno=0;
   char *wd=realpath(".", nullptr);
 
-  if(wd == nullptr || errno != 0)
+  if(wd == nullptr)
     throw system_exceptiont(
       std::string("realpath failed: ") + std::strerror(errno));
 

src/util/tempdir.cpp

@@ -93,7 +93,7 @@ std::string get_temporary_directory(const std::string &name_template)
   errno = 0;
   char *wd = realpath(td, nullptr);
 
-  if(wd == nullptr || errno != 0)
+  if(wd == nullptr)
     throw system_exceptiont(
       std::string("realpath failed: ") + std::strerror(errno));