[Build] Resolved Most IPO Warnings

VTR is built with IPO by default. IPO tends to reveal false warnings in
the compiler. This was causing many warnings when VTR was built by
default.

Most of these warnings were coming from libarchfpga due to how it
allocates arrays. Suppressed these warnings when IPO is turned on.

There are still link-time warnings coming from CapNProto; however, since
this library is external, it is a harder to supress these warnings. We
could suppress the warnings by globally setting the link option to
ignore the warning, but that may be overkill.

Author: AlexandreSinger

libs/libarchfpga/CMakeLists.txt

@@ -53,6 +53,18 @@ endif()
 
 target_compile_definitions(libarchfpga PUBLIC ${INTERCHANGE_SCHEMA_HEADERS})
 
+# Supress IPO link warnings if IPO is enabled
+get_target_property(LIBARCHFPGA_USES_IPO libarchfpga INTERPROCEDURAL_OPTIMIZATION)
+if(LIBARCHFPGA_USES_IPO)
+    # LibArchFPGA uses ints in many of its data structures instead of size_t for
+    # the size of arrays which are used to allocate arrays. At link-time, this
+    # causes many false allocation warnings when IPO is enabled.
+    # In order to suppress these warnings, we must make this PUBLIC so that not
+    # only we suppress the warning for libarchfpga, but also anything else that
+    # links with it.
+    target_link_options(libarchfpga PUBLIC -Wno-alloc-size-larger-than)
+endif()
+
 #Create the test executable
 add_executable(read_arch ${READ_ARCH_EXEC_SRC})
 target_link_libraries(read_arch libarchfpga)