Remove Folly dependency from MappedFileBuffer.cpp

Summary:
Folly was just used for some error checking, so do it manually to avoid
adding Folly as a dependency.

Reviewed By: kodafb

Differential Revision: D22177031

fbshipit-source-id: 65f4212047d50d61adcb888a7751298e5e24a6de

android/test/java/com/facebook/hermes/test/MappedFileBuffer.cpp

@@ -8,20 +8,25 @@
 #include <MappedFileBuffer.h>
 
 #include <fcntl.h>
-#include <folly/Exception.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <memory>
+#include <system_error>
 
 namespace facebook {
 namespace jsi {
 namespace jni {
 
 MappedFileBuffer::MappedFileBuffer(const std::string &fileName) {
-  folly::checkUnixError(fd_ = open(fileName.c_str(), O_RDONLY));
+  fd_ = open(fileName.c_str(), O_RDONLY);
+  if (fd_ < 0) {
+    throw std::system_error(errno, std::system_category(), "open failed");
+  }
   struct stat statbuf;
-  folly::checkUnixError(fstat(fd_, &statbuf));
+  if (fstat(fd_, &statbuf) < 0) {
+    throw std::system_error(errno, std::system_category(), "fstat failed");
+  }
   size_ = statbuf.st_size;
   void *bytecodeFileMap = mmap(
       /*address*/ nullptr, size_, PROT_READ, MAP_PRIVATE, fd_, /*offset*/ 0);
@@ -30,8 +35,12 @@ MappedFileBuffer::MappedFileBuffer(const std::string &fileName) {
 }
 
 MappedFileBuffer::~MappedFileBuffer() {
-  folly::checkUnixError(munmap(data_, size_));
-  folly::checkUnixError(close(fd_));
+  if (munmap(data_, size_) < 0) {
+    assert(false && "Failed to munmap MappedFileBuffer");
+  }
+  if (close(fd_) < 0) {
+    assert(false && "Failed to close MappedFileBuffer");
+  }
 }
 
 } // namespace jni