linux-*: use upstream gcc6 [skip ci]

Adjust HOSTCC to work with Alpine's version.

device/linux-infocus-flatfish/APKBUILD

@@ -2,7 +2,7 @@
 
 pkgname="linux-infocus-flatfish"
 pkgver=3.3.0
-pkgrel=0
+pkgrel=1
 pkgdesc="InFocus New Tab F1 kernel fork"
 arch="armhf"
 _carch="arm"
@@ -17,7 +17,7 @@ makedepends="perl sed installkernel bash gmp-dev bc linux-headers elfutils-dev g
 # well. See <https://postmarketos.org/vendorkernel> for instructions.
 if [ "${CC:0:5}" != "gcc6-" ]; then
 	CC="gcc6-$CC"
-	HOSTCC="gcc6-gcc"
+	HOSTCC="gcc-6"
 	CROSS_COMPILE="gcc6-$CROSS_COMPILE"
 fi