gnucash-on-windows master: Fix building bdw-gc on gcc-10.1.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash-on-windows/commit/e49fa471 (commit)
	from  https://github.com/Gnucash/gnucash-on-windows/commit/bf76f124 (commit)



commit e49fa4719fd1c386c745ccd15f693207aa124ba8
Author: John Ralls <jralls at ceridwen.us>
Date:   Sat May 23 14:14:40 2020 -0700

    Fix building bdw-gc on gcc-10.1.
    
    See https://gcc.cnu.org/gcc-10/porting_to.html, "Default to
    -fno-common." for an explanation.



Summary of changes:
 jhbuildrc.in | 6 ++++++
 1 file changed, 6 insertions(+)