As all invokes all-recursive which uses sub-makes to invoke all-am, the
resulting makefile wants to build libusb-1.0.la twice. In non-parallel builds
the second attempt is skipped as the target already exists, but in highly
parallel builds it's likely that two makes will be building libusb-1.0.la at the
same time.

Solve this by removing the explicit all target, which as libusb-1.0.dll isn't
built under Linux is redundant anyway.

Upstream-Status: Pending
Signed-off-by: Ross Burton <ross.burton@intel.com>

diff --git a/libusb/Makefile.am b/libusb/Makefile.am
index 0cab0a0..c880213 100644
--- a/libusb/Makefile.am
+++ b/libusb/Makefile.am
@@ -1,2 +0,0 @@
-all: libusb-1.0.la libusb-1.0.dll
-