build: fix ARM vfp naming in configure script for older ARM processors

[mnkhouri]

This commit changes the default vfp name from 'vfpv2' to 'vfp', affecting
builds for ARM architectures older than ARMv7.

Valid options for 'arm_fpu' in gcc do NOT include 'vfpv2', causing gcc to
quit with error: unrecognized argument in option ‘-mfpu=vfpv2’ when
using the configure script with --dest-cpu=arm.

Gyp also expects only vfp, vfpv3-d16, vfpv3, neon.

GCC reference for the -mfpu= option:
https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html
Gyp makefile reference:
https://github.com/nodejs/node/blob/v4.0.0/Makefile.build#L173

[mnkhouri]

To reproduce:
./configure --dest-cpu=arm --dest-os=linux --with-arm-float-abi softfp && make

My toolchain:
export AR=arm-linux-gnueabi-ar CC=arm-linux-gnueabi-gcc-4.9 CXX=arm-linux-gnueabi-g++-4.9 LINK=arm-linux-gnueabi-g++-4.9

[rvagg]

/ @nodejs/build

[bnoordhuis]

LGTM apart from the commit log: the first line should be <= 50 columns, ones after that <= 72.

arm_fpu is only used by V8's gyp files. I speculate that the way they use it has changed in recent versions, resulting in this breakage.

[mnkhouri]

Amended commit message to match column guidelines

[Fishrock123]

pinging @nodejs/build again

[bnoordhuis]

I think this has been obsoleted by 17665af.

[Fishrock123]

Hmm, maybe? It's possible that the default should still be changed? 17665af#diff-e2d5a00791bce9a01f99bc6fd613a39dR618

[bnoordhuis]

Maybe not obsoleted then but it certainly needs rebasing.

[ronkorving]

Is this still relevant? Does it still need rebasing? Ping @mnkhouri

[mnkhouri]

Someone beat me to the punch: 84dea1b

Closing this PR