gcc9: Add no-sys-dir patch for RISC-V (#154230)

Same as in gcc{10,11} (#147942).

pkgs/development/compilers/gcc/9/default.nix

@@ -82,6 +82,7 @@ let majorVersion = "9";
       ++ optional (targetPlatform != hostPlatform) ../libstdc++-target.patch
       ++ optional targetPlatform.isNetBSD ../libstdc++-netbsd-ctypes.patch
       ++ optional noSysDirs ../no-sys-dirs.patch
+      ++ optional (noSysDirs && hostPlatform.isRiscV) ../no-sys-dirs-riscv-gcc9.patch
       /* ++ optional (hostPlatform != buildPlatform) (fetchpatch { # XXX: Refine when this should be applied
         url = "https://git.busybox.net/buildroot/plain/package/gcc/${version}/0900-remove-selftests.patch?id=11271540bfe6adafbc133caf6b5b902a816f5f02";
         sha256 = ""; # TODO: uncomment and check hash when available.

pkgs/development/compilers/gcc/no-sys-dirs-riscv-gcc9.patch

@@ -0,0 +1,17 @@
+diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
+index 701f5ea1544..8de333caf54 100644
+--- a/gcc/config/riscv/riscv.h
++++ b/gcc/config/riscv/riscv.h
+@@ -886,11 +886,7 @@ extern unsigned riscv_stack_boundary;
+   "%{mabi=lp64f:lp64f}" \
+   "%{mabi=lp64d:lp64d}" \
+ 
+-#define STARTFILE_PREFIX_SPEC 			\
+-   "/lib" XLEN_SPEC "/" ABI_SPEC "/ "		\
+-   "/usr/lib" XLEN_SPEC "/" ABI_SPEC "/ "	\
+-   "/lib/ "					\
+-   "/usr/lib/ "
++#define STARTFILE_PREFIX_SPEC ""
+ 
+ /* ISA constants needed for code generation.  */
+ #define OPCODE_LW    0x2003