Move exception to header

Otherwise, it obviously can't be caught by users of the ElfFile class.

include/linuxdeploy/core/elf.h

@@ -10,6 +10,12 @@
 namespace linuxdeploy {
     namespace core {
         namespace elf {
+            // thrown by constructor if file is not an ELF file
+            class ElfFileParseError : public std::runtime_error {
+                public:
+                    explicit ElfFileParseError(const std::string& msg) : std::runtime_error(msg) {}
+            };
+
             class ElfFile {
                 private:
                     class PrivateData;

src/core/elf.cpp

@@ -17,12 +17,6 @@ namespace bf = boost::filesystem;
 namespace linuxdeploy {
     namespace core {
         namespace elf {
-            // thrown by constructor if file is not an ELF file
-            class ElfFileParseError : public std::runtime_error {
-                public:
-                    explicit ElfFileParseError(const std::string& msg) : std::runtime_error(msg) {}
-            };
-
             class ElfFile::PrivateData {
                 public:
                     const bf::path path;