compiling libroot with DEBUG=1 failes
$ DEBUG=1 jam libroot.so
...patience...
...patience...
...found 2621 target(s)...
...updating 1 target(s)...
Link generated/objects/haiku/x86/debug_1/system/libroot/libroot.so
generated/objects/haiku/x86/debug_1/system/libroot/posix/glibc/stdio-common/posix_gnu_stdio.o(.text+0x4c23):
In function `printf_fphex':
/Develop/haiku/src/system/libroot/posix/glibc/stdio-common/printf_fphex.c:203:
undefined reference to `signbitl'
generated/objects/haiku/x86/debug_1/system/libroot/posix/glibc/stdio-common/posix_gnu_stdio.o(.text+0x4d43):/Develop/haiku/src/system/libroot/posix/glibc/stdio-common/printf_fphex.c:242:
undefined reference to `signbit'
collect2: ld returned 1 exit status
fixed in revision 16371