toolchain/crosstool-ng: vendor part of tuple should be 'buildroot'

Since 11017f081fc5b034e680d89eaea729c19f450e01, the Crosstool-ng
backend generates toolchains that have a prefix inconsistent with what
Buildroot expects. Buildroot expects a "buildroot" vendor name, while
Crosstool-NG builds toolchain with the "unknown" vendor name.

This is causing build failure such as:

  http://autobuild.buildroot.org/results/15b2c0e50a81b86dd13af684c9254df2bc0df8de/build-end.log

Fix this by changing the vendor part of the tuple used by Crosstool-NG
to "buildroot".

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/toolchain-crosstool-ng/crosstool-ng.mk

@@ -201,7 +201,7 @@ CTNG_FIX_DOT_CONFIG_SED += s:^(|\# )(CT_ARCH_[BL]E).*:\# \2 is not set:;
 CTNG_FIX_DOT_CONFIG_SED += s:^\# (CT_ARCH_$(CTNG_ENDIAN)) is not set:\1=y:;
 CTNG_FIX_DOT_CONFIG_SED += s:^(|\# )(CT_ARCH_(32|64)).*:\# \2 is not set:;
 CTNG_FIX_DOT_CONFIG_SED += s:^\# (CT_ARCH_$(CTNG_BIT)) is not set:\1=y:;
-CTNG_FIX_DOT_CONFIG_SED += s:^(CT_TARGET_VENDOR)=.*:\1="unknown":;
+CTNG_FIX_DOT_CONFIG_SED += s:^(CT_TARGET_VENDOR)=.*:\1="buildroot":;
 CTNG_FIX_DOT_CONFIG_SED += s:^(CT_TARGET_ALIAS)=.*:\1="$(ARCH)-linux":;
 CTNG_FIX_DOT_CONFIG_SED += s:^(CT_TOOLCHAIN_PKGVERSION)="(.*)":\1="buildroot $(BR2_VERSION_FULL)":;
 ifneq ($(call qstrip,$(BR2_USE_MMU)),)