depends: Avoid using the -ffile-prefix-map compiler option

The `-ffile-prefix-map` compiler option implicitly enables
`-fprofile-prefix-map` in GCC or `-fcoverage-prefix-map` in Clang, which
can cause issues with coverage builds.

This change ensures that only the options necessary for build
reproducibility are applied.

depends/packages/capnp.mk

@@ -9,7 +9,7 @@ define $(package)_set_vars :=
   $(package)_config_opts := -DBUILD_TESTING=OFF
   $(package)_config_opts += -DWITH_OPENSSL=OFF
   $(package)_config_opts += -DWITH_ZLIB=OFF
-  $(package)_cxxflags += -ffile-prefix-map=$$($(package)_extract_dir)=/usr
+  $(package)_cxxflags += -fdebug-prefix-map=$($(package)_extract_dir)=/usr -fmacro-prefix-map=$($(package)_extract_dir)=/usr
 endef
 
 define $(package)_config_cmds