bpf: avoid issues with CO-RE and -gtoggle

Compiling a BPF program with CO-RE relocations (and BTF) while also
passing -gtoggle led to an inconsistent state where CO-RE support was
enabled but BTF would not be generated, and this was not caught by the
existing option parsing.  This led to an ICE when generating the CO-RE
relocation info, since BTF is required for CO-RE.

Update bpf_option_override to avoid this case, and add a few tests for
the interactions of these options.

gcc/
	* config/bpf/bpf.cc (bpf_option_override): Improve handling of CO-RE
	options to avoid issues with -gtoggle.

gcc/testsuite/
	* gcc.target/bpf/core-options-1.c: New test.
	* gcc.target/bpf/core-options-2.c: Likewise.
	* gcc.target/bpf/core-options-3.c: Likewise.

gcc/config/bpf/bpf.cc

@@ -192,7 +192,8 @@ bpf_option_override (void)
   init_machine_status = bpf_init_machine_status;
 
   /* BPF CO-RE support requires BTF debug info generation.  */
-  if (TARGET_BPF_CORE && !btf_debuginfo_p ())
+  if (TARGET_BPF_CORE
+      && (!btf_debuginfo_p () || (debug_info_level < DINFO_LEVEL_NORMAL)))
     error ("BPF CO-RE requires BTF debugging information, use %<-gbtf%>");
 
   /* BPF applications always generate .BTF.ext.  */
@@ -215,7 +216,9 @@ bpf_option_override (void)
 
   /* -gbtf implies -mcore when using the BPF backend, unless -mno-co-re
      is specified.  */
-  if (btf_debuginfo_p () && !(target_flags_explicit & MASK_BPF_CORE))
+  if (btf_debuginfo_p ()
+      && (debug_info_level >= DINFO_LEVEL_NORMAL)
+      && !(target_flags_explicit & MASK_BPF_CORE))
     target_flags |= MASK_BPF_CORE;
 
   /* Determine available features from ISA setting (-mcpu=).  */

gcc/testsuite/gcc.target/bpf/core-options-1.c

+/* -gbtf for the BPF target should enable CO-RE support automatically.  */
+/* { dg-do compile } */
+/* { dg-options "-gbtf" } */
+
+struct A {
+  int x;
+  int y;
+  char c;
+};
+
+int
+foo (struct A *a) {
+  int y = __builtin_preserve_access_index (a->y);
+  return y;
+}

gcc/testsuite/gcc.target/bpf/core-options-2.c

+/* { dg-do compile } */
+/* { dg-options "-gbtf -gtoggle" } */
+
+struct A {
+  int x;
+  int y;
+  char c;
+};
+
+int
+foo (struct A *a) {
+  int y = __builtin_preserve_access_index (a->y); /* { dg-error "BPF CO-RE is required" } */
+  return y;
+}

gcc/testsuite/gcc.target/bpf/core-options-3.c

+/* This combination of options tries to enable CO-RE without BTF, and should
+   produce an error.  */
+/* { dg-do compile } */
+/* { dg-options "-gbtf -gtoggle -mco-re" } */
+/* { dg-excess-errors "BPF CO-RE requires BTF debugging information" } */