Trying to rebuild glibc with -DMALLOC_DEBUG=1

[Paul Dufresne]

I am trying to rebuild glibc with -DMALLOC_DEBUG=1

$ DEB_CFLAGS_APPEND="-DMALLOC_DEBUG=1" dpkg-buildpackage -b -uc -us -nc
(-nc is because I am stopping the build sometimes to check the output)

But I don't see "-DMALLOC_DEBUG=1" in the generated compiled lines... like in:
i686-gnu-gcc-10 
/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd/RPC_termctty_open_terminal.c
 -c -std=gnu11 -fgnu89-inline  -pipe -O2 -g 
-fdebug-prefix-map=/home/paul/malloc/glibc-2.31=. -Wall -Wwrite-strings -Wundef 
-fmerge-all-constants -frounding-math -fstack-protector-strong -Wno-parentheses 
-Wstrict-prototypes -Wold-style-definition -fmath-errno    -Wa,-mtune=i686      
 -isystem /home/paul/malloc/glibc-2.31/debian/include  -I../include 
-I/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd  
-I/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc  
-I../sysdeps/mach/hurd/i386  -I../sysdeps/mach/hurd/x86  
-I../sysdeps/mach/hurd/i386/htl  -I../sysdeps/mach/hurd/htl  
-I../sysdeps/hurd/htl  -I../sysdeps/mach/htl  -I../sysdeps/htl  
-I../sysdeps/pthread  -I../sysdeps/i386/htl  -I../sysdeps/mach/hurd  
-I../sysdeps/gnu  -I../sysdeps/unix/bsd  -I../sysdeps/unix/inet  
-I../sysdeps/mach/i386  -I../sysdeps/mach/include -I../sysdeps/mach  
-I../sysdeps/i386/i686/fpu  -I../sysdeps/i386/i686  -I../sysdeps/i386/fpu  
-I../sysdeps/x86/fpu/include -I../sysdeps/x86/fpu  -I../sysdeps/i386  
-I../sysdeps/x86  -I../sysdeps/wordsize-32  -I../sysdeps/ieee754/float128  
-I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96  
-I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32  
-I../sysdeps/hurd/include -I../sysdeps/hurd  -I../sysdeps/unix  
-I../sysdeps/posix  -I../sysdeps/ieee754  -I../sysdeps/generic -I../hurd 
-I/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd/ -I../mach 
-I/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/mach/ -I.. -I../libio 
-I. -nostdinc -isystem /usr/lib/gcc/i686-gnu/10/include -isystem 
/home/paul/malloc/glibc-2.31/debian/include  -D_LIBC_REENTRANT -include 
/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/libc-modules.h 
-DMODULE_NAME=libhurduser -include ../include/libc-symbols.h  -DPIC     
-DTOP_NAMESPACE=glibc -o 
/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd/RPC_termctty_open_terminal.o
 -MD -MP -MF 
/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd/RPC_termctty_open_terminal.o.dt
 -MT 
/home/paul/malloc/glibc-2.31/build-tree/hurd-i386-libc/hurd/RPC_termctty_open_terminal.o

with the hello packsage I do see the -DMALLOC_DEBUG=1

I admit glibc is a much more complex than hello... but it is also why I want to 
make sure I do it right because it is a bit long to compile.

Also, I am a bit confused, that if I use ~/.config/dpkg/buildflags.conf
I see changes in dpkg-buildflags output... but the man say is no more 
automatically exported... and so it is unclear
what I need to do for it to be applied to the dpkg-buildpackage command.