In a combined gcc 4.6 + binutils tree configured with
-with-build-config=bootstrap-lto, I got

make -j8
...
...
libtool: link: /export/build/gnu/gcc-lto/build-x86_64-linux/./prev-gcc/xgcc
-B/export/build/gnu/gcc-lto/build-x86_64-linux/./prev-gcc/
-B/usr/gcc-4.6.0/x86_64-unknown-linux-gnu/bin/
-B/usr/gcc-4.6.0/x86_64-unknown-linux-gnu/bin/
-B/usr/gcc-4.6.0/x86_64-unknown-linux-gnu/lib/ -isystem
/usr/gcc-4.6.0/x86_64-unknown-linux-gnu/include -isystem
/usr/gcc-4.6.0/x86_64-unknown-linux-gnu/sys-include -W -Wall
-Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -g -O2
-flto=jobserver -fuse-linker-plugin -frandom-seed=1 -o .libs/as-new app.o as.o
atof-generic.o compress-debug.o cond.o depend.o dwarf2dbg.o dw2gencfi.o ecoff.o
ehopt.o expr.o flonum-copy.o flonum-konst.o flonum-mult.o frags.o hash.o
input-file.o input-scrub.o listing.o literal.o macro.o messages.o output-file.o
read.o remap.o sb.o stabs.o subsegs.o symbols.o write.o tc-i386.o obj-elf.o
atof-ieee.o  -L/export/build/gnu/gcc-lto/build-x86_64-linux/./ld
../opcodes/.libs/libopcodes.so
-L/export/build/gnu/gcc-lto/build-x86_64-linux/opcodes/../libiberty/pic
../bfd/.libs/libbfd.so
-L/export/build/gnu/gcc-lto/build-x86_64-linux/bfd/../libiberty/pic -liberty
../libiberty/libiberty.a -lz -Wl,-rpath -Wl,/usr/gcc-4.6.0/lib
make[3]: *** read jobs pipe EOF.  Stop.
make[3]: *** Waiting for unfinished jobs....
lto-wrapper: make returned 2 exit status
lto-wrapper failedcollect2: ld returned 1 exit status
make[2]: *** [as-new] Error 1
make[2]: Leaving directory `/export/build/gnu/gcc-lto/build-x86_64-linux/gas'
make[1]: *** [all-recursive] Error 1

Gcc manual says

---
     You can also specify `-flto=jobserver' to use GNU make's job
     server mode to determine the number of parallel jobs. This is
     useful when the Makefile calling GCC is already executing in
     parallel.  The parent Makefile will need a `+' prepended to the
     command recipe for this to work. This will likely only work if
     `MAKE' is GNU make.
---

Binutils Makefiles don't have `+' and failed.

[hjl@gnu-6 binutils]$ grep "^LINK" */Makefile.*
bfd/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
binutils/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
gas/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
gold/Makefile.in:LINK = $(CCLD) $(AM_CFLAGS) $(CFLAGS) $(AM_LDFLAGS) $(LDFLAGS) -o $@
gprof/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
ld/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
opcodes/Makefile.am:LINK_FOR_BUILD = $(CC_FOR_BUILD) $(CFLAGS_FOR_BUILD) \
opcodes/Makefile.in:LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
opcodes/Makefile.in:LINK_FOR_BUILD = $(CC_FOR_BUILD) $(CFLAGS_FOR_BUILD) \
[hjl@gnu-6 binutils]$ 

We need to prepend `+'.