qrcodegen: add missing patch

srcpkgs/qrcodegen/patches/cpp_Makefile.patch

@@ -0,0 +1,20 @@
+Source: @pullmoll
+Upstream: no
+Reason: sanitizer does not link and is missing for musl; enable PIC
+
+--- cpp/Makefile	2019-07-16 01:16:50.000000000 +0200
++++ cpp/Makefile	2020-01-29 22:57:19.157930868 +0100
+@@ -29,12 +29,7 @@
+ # - CXXFLAGS: Any extra user-specified compiler flags (can be blank).
+ 
+ # Mandatory compiler flags
+-CXXFLAGS += -std=c++11
+-# Diagnostics. Adding '-fsanitize=address' is helpful for most versions of Clang and newer versions of GCC.
+-CXXFLAGS += -Wall -fsanitize=undefined
+-# Optimization level
+-CXXFLAGS += -O1
+-
++CXXFLAGS += -std=c++11 -Wall -fPIC
+ 
+ # ---- Controlling make ----
+