How to enforce the struct bit order with the GCC compiler?

I was wondering if there is a GCC C Compiler directive that allows me to determine the bit order for packing of a structure? Something to the likes of:

#pragma bit_order left

The rationale for such a need is that I have the following structure:

struct {       union {             unsigned char BYTE;             struct {                 unsigned char B0: 1;                 unsigned char B1: 1;                 unsigned char B2: 1;                 unsigned char B3: 1;                 unsigned char B4: 4;             }BIT;       }ITEM;} myStruct;

With this structure, I would like the compiler to pack it this way:

Bit order: | 7  6  5  4  3  2  1  0 |Label:     |B0 B1 B2 B3 B4 B5 B6 B7 |

Rather than how GCC does it:

Bit order: | 7  6  5  4  3  2  1  0 |Label:     |B7 B6 B5 B4 B3 B2 B1 B0 |

I am dealing with MCUs that have huge header files that have structures that compute bit offsets according to stipulated hardware addresses. I am hoping that there is a compiler directive in GCC C Compiler that does the bit order swap for me before I attempt the flip all the fields in the manufacturer supplied file.