Improve dotdot workaround when src begins with '/'

There are some source files in our tree that use some text processing to
find source files, and end up with source file names that look like:

  /../../dir/file.c

This isn't fixed by our dotdot workarounds because the filename doesn't
start with '../', so strip the initial '/' from any source files, since
they are all relative to $(LOCAL_PATH) anyways.

Bug: 32514380
Test: Build internal source with this problem
Test: Compare build-aosp_angler.ninja before/after
Change-Id: If869419c3d3ba35d55f6e19d9332515695e47d24
diff --git a/core/binary.mk b/core/binary.mk
index 0f9ef2f..28ac56f 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -324,6 +324,10 @@
 endif
 my_src_files := $(filter-out $(my_src_files_exclude),$(my_src_files))
 
+# Strip '/' from the beginning of each src file. This helps the ../ detection in case
+# the source file is in the form of /../file
+my_src_files := $(patsubst /%,%,$(my_src_files))
+
 my_clang := $(strip $(LOCAL_CLANG))
 ifdef LOCAL_CLANG_$(my_32_64_bit_suffix)
 my_clang := $(strip $(LOCAL_CLANG_$(my_32_64_bit_suffix)))