Comment 2 for bug 1855994

Our remaining Delta was only for FTBFS issues with glibc/gcc:

 TEST_GCC_VER_9 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 9)
 ifeq ($(TEST_GCC_VER_9),1)
- CFLAGS += -Wno-error=address-of-packed-member -Wno-stringop-truncation
+ CFLAGS += -Wno-error=address-of-packed-member -Wno-stringop-truncation -Wno-cpp -Wno-error=format-truncation
 endif

Changelog:
+ - debian/rules: Work around FTBFS with glibc 2.30 with -Wno-cpp
+ - debian/rules: Work around FTBFS with gcc9 -Wno-error=format-truncation

The real new source might have those fixed already without the need for it?!
Giving a build in focal-proposed a try...