How do I get startup code that I have edited to compile?

I am trying to edit the startup code for the MCUXpresso LPC51U68 board so that I can flash an enhanced image to the board See instructions in section 3.5.6 (pg. 17) of this user manual (NXP_LPC51U68_UM). I changed the bolded lines from the user manual in the startup code that I downloaded from the SDK for the LPC51U68 board (on NXP's website). I wrote the IMAGEHEADER_T fuction from the user manual in the startup code also.

My edits to the startup code ended up looking like this:

__attribute__ ((used, section(".isr_vector")))
void (* const g_pfnVectors[])(void) = {
    // Core Level - CM0P
    &_vStackTop,                       // The initial stack pointer
    ResetISR,                          // The reset handler
    NMI_Handler,                       // The NMI handler
    HardFault_Handler,                 // The hard fault handler
    0,                                 // Reserved
    0,                                 // Reserved
    0,                                 // Reserved
    __valid_user_code_checksum,        // LPC MCU checksum
    0,                                 // ECRP
    (void*) 0xEDDC9494,                // Enhanced image marker            (This was added)
    imageHeader,                       // Pointer to enhanced image header (This was added)
    SVC_Handler,                       // SVCall handler
    0,                                 // Reserved
    0,                                 // Reserved
    PendSV_Handler,                    // The PendSV handler
    SysTick_Handler,                   // The SysTick handler

and this is the definition for the image header (should be exactly as appears in the user manual):

/*Image Header*/
const IMAGEHEADER_T imageHeader = {
    IMAGE_ENH_BLOCK_MARKER, //Required marker for image header
        IMG_NO_CRC, //No  CRC, makes development easier
        0x00000000, //crc32_len
        0x00000000, //crc32_val
        0x00000000  //version

HOWEVER, after making these edits I found that the startup code won't compile. When I checked the memory at offset 0x24 to see if it receive the enhanced image flag 0xEDDC9494, it wasn't there. I tried typing some garbage in the startup code and then building and compiling to see if I got an error and there was no error. How do I get my startup code to compile???

If i create a default LPC51U68 SDK project with MCUXpresso there are no defines for the mentioned structs and values. So you need to do it yourself.

    //*****************************************************************************
    //*****************************************************************************
    #define IMAGE_SINGLE_ENH_SIG    0xEDDC9494
    #define IMAGE_ENH_BLOCK_MARKER  0xFEEDA5A5
    #define IMG_NORMAL              0
    #define IMG_NO_CRC              1

    typedef struct IMAGEHEADER_STRUCT
    {
        unsigned int header_marker;
        unsigned int img_type;
        unsigned int crc32_len;
        unsigned int crc32_val;
        unsigned int version;
    } IMAGEHEADER_T;

    /* Image header */
    const IMAGEHEADER_T imageHeader = {
        IMAGE_ENH_BLOCK_MARKER, /* Required marker for image header */
        IMG_NO_CRC,             /* No CRC, makes development easier */
        0x00000000,             /* crc32_len */
        0x00000000,             /* crc32_val */
        0x00000000              /* version */
    };

    //*****************************************************************************
    // The vector table.
    // This relies on the linker script to place at correct location in memory.
    //*****************************************************************************
    extern void (* const g_pfnVectors[])(void);
    extern void * __Vectors __attribute__ ((alias ("g_pfnVectors")));

    __attribute__ ((used, section(".isr_vector")))
    void (* const g_pfnVectors[])(void) = {
        // Core Level - CM0P
        &_vStackTop,                       // The initial stack pointer
        ResetISR,                          // The reset handler
        NMI_Handler,                       // The NMI handler
        HardFault_Handler,                 // The hard fault handler
        0,                                 // Reserved
        0,                                 // Reserved
        0,                                 // Reserved
        __valid_user_code_checksum,        // LPC MCU checksum
        0,                                 // ECRP
        (void*) IMAGE_SINGLE_ENH_SIG,      // Enhanced image marker            @0x24
        (void*) &imageHeader,              // Pointer to enhanced image header @0x28
        SVC_Handler,                       // SVCall handler
        0,                                 // Reserved
        0,                                 // Reserved
        PendSV_Handler,                    // The PendSV handler
        SysTick_Handler,                   // The SysTick handler

        // Chip Level - LPC51U68
        ...

    }; /* End of g_pfnVectors */

This should compile. However i dont know whats the enhanced image is for.