qemu: move build outside of kernel dir to avoid kernel's make clean

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

.gitignore

@@ -1,7 +1,9 @@
 cscope.out
 *.o
+*.d
 *.ko
 *.mod.c
+src/tools/wg
 Module.symvers
 *.cmd
 .tmp_versions
@@ -9,3 +11,11 @@ Module.symvers
 modules.order
 modules.builtin
 maint/
+qemu-build/
+src/tests/qemu/distfiles/
+*.id0
+*.id1
+*.id2
+*.nam
+*.til
+*.pro.user

src/.gitignore

@@ -1,3 +0,0 @@
-*.d
-*.o
-wg