mesa: enable 17.1.7 on gcc2_x86, patch configure's llvm test.

sys-libs/mesa/mesa-17.1.7.recipe

@@ -12,7 +12,7 @@ CHECKSUM_SHA256="69f472a874b1122404fa0bd13e2d6bf87eb3b9ad9c21d2f39872a96d83d9e5f
 PATCHES="mesa-$portVersion.patchset"
 
 ARCHITECTURES="!x86_gcc2 x86 x86_64 ?arm ?ppc"
-SECONDARY_ARCHITECTURES="?x86"
+SECONDARY_ARCHITECTURES="x86"
 
 PROVIDES="
 	mesa$secondaryArchSuffix = $portVersion
@@ -54,12 +54,14 @@ REQUIRES_swpipe="
 BUILD_REQUIRES="
 	haiku${secondaryArchSuffix}_devel
 	devel:libz$secondaryArchSuffix
-	llvm${secondaryArchSuffix} >= 5
+	devel:libLLVM_5.0$secondaryArchSuffix
 	"
 BUILD_PREREQUIRES="
 	cmd:aclocal
 	cmd:autoconf
 	cmd:automake
+	cmd:llvm_config
+	cmd:egrep
 	cmd:gcc$secondaryArchSuffix
 	cmd:ld$secondaryArchSuffix
 	cmd:libtoolize$secondaryArchSuffix
@@ -75,7 +77,12 @@ BUILD()
 	fi
 
 	autoreconf -fi
+	# for whatever reason, the llvm_require_version function is busted, so we
+	# manually patch it here
+	sed -i 's@"\$LLVM_VERSION_MAJOR" -gt "\$llvm_target_version_major"@true@' configure
+	sed -i 's@-DHAVE_LLVM=0x0\$LLVM_VERSION_INT@-DHAVE_LLVM=0x0500@' configure
 	runConfigure ./configure \
+		--enable-llvm \
 		--disable-dri \
 		--disable-glx \
 		--disable-glx-tls \