Coroutines backports.

[Iain Sandoe]

Hi, 

I’ve backported the following fixes 
to GCC 11

14ed21f8749ae359690d9c4a69ca38cc45d0d1b0, 
8406ed9af2655479a9c8469d7acca2cf5784f5d6,
21b4d0ef543d68187d258415b51d0d6676af89fd, 
88974974d8188cf12e87e4ad3d23a8cbdd557f0e,
a45a7ecdf34311587daa2e90cc732adcefac447b, 
addf167a23f61c0ec97f6e71577a0623f3fc13e7,
c5a735fa9df7eca4666c8da5e51ed9c5ab7cc81a, 
70ee703c479081ac2ea67eb67041551216e66783,
fae627162d5f8cfb273b10349883eeb74baaa43f

which constitutes as far as we’ve got at present with debugging support (PR 
99215)

To GCC-10

3bcf19215d88e6ec33d283352c52005f02dbc784, 
0d5db79a61af150cba48612c9fbc3267262adb93,
d5b1bb0d197f9141a0f0e510f8d1b598c3df9552, 
237ab3ee49e2f3110accfcc03b6c0df8b4889f15,

which fixes PR95520 and some minor issues.

thanks
Iain