libcilkrts breaks non-bootstrap build

[Tom de Vries]

Hi,

When configuring a gcc build with "--disable-bootstrap --enable-languages=c" I
run into this error:
...
libtool: compile:  g++
-B/home/vries/gcc_versions/devel/lean-c/install/x86_64-unknown-linux-gnu/bin/
-B/home/vries/gcc_versions/devel/lean-c/install/x86_64-unknown-linux-gnu/lib/
-isystem
/home/vries/gcc_versions/devel/lean-c/install/x86_64-unknown-linux-gnu/include
-isystem
/home/vries/gcc_versions/devel/lean-c/install/x86_64-unknown-linux-gnu/sys-include
"-DPACKAGE_NAME=\"Cilk Runtime Library\""
-DPACKAGE_TARNAME=\"cilk-runtime-library\" -DPACKAGE_VERSION=\"2.0\"
"-DPACKAGE_STRING=\"Cilk Runtime Library 2.0\""
-DPACKAGE_BUGREPORT=\"cilk@intel.com\" -DPACKAGE_URL=\"\"
-DPACKAGE=\"cilk-runtime-library\" -DVERSION=\"2.0\" -DSTDC_HEADERS=1
-DHAVE_SYS_TYPES_H=1 -DHAVE_SYS_STAT_H=1 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1
-DHAVE_MEMORY_H=1 -DHAVE_STRINGS_H=1 -DHAVE_INTTYPES_H=1 -DHAVE_STDINT_H=1
-DHAVE_UNISTD_H=1 -DHAVE_ALLOCA_H=1 -DHAVE_ALLOCA=1 -DHAVE_DLFCN_H=1
-DLT_OBJDIR=\".libs/\" -I. -I/home/vries/gcc_versions/devel/src/libcilkrts
-I/home/vries/gcc_versions/devel/src/libcilkrts/include
-I/home/vries/gcc_versions/devel/src/libcilkrts/runtime
-I/home/vries/gcc_versions/devel/src/libcilkrts/runtime/config/x86
-DIN_CILK_RUNTIME=1 -D_Cilk_spawn= -D_Cilk_sync= -D_Cilk_for=for -fcilkplus -g3
-O0 -dH -D_GNU_SOURCE -MT bug.lo -MD -MP -MF .deps/bug.Tpo -c
/home/vries/gcc_versions/devel/src/libcilkrts/runtime/bug.cpp  -fPIC -DPIC -o
.libs/bug.o
g++: error: unrecognized command line option ‘-fcilkplus’
make[2]: *** [bug.lo] Error 1
make[2]: Leaving directory
`/home/vries/gcc_versions/devel/lean-c/build/x86_64-unknown-linux-gnu/libcilkrts'
...

The error occurs because the compiler doesn't support -fcilkplus.

Should configure disable libcilkplus when c++ is not enabled?

I see the same error with "--disable-bootstrap --enable-languages=c,c++". Should
configure test the compiler for support of -fcilkplus and disable libcilkplus if
not?

Thanks,
- Tom