[PATCH v1] objtool: Validate disassembler headers in libopcodes probe

[Ulises Mendez Martinez <umendez@google.com>]

commit 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
tested for libopcodes availability by linking a test snippet with a forward
declaration of disassemble_init_for_target().

However, testing symbol linkage with an extern declaration only verifies
the presence of the library (.so/.a) and bypasses checking for development
headers (binutils-dev). On systems where libopcodes is present without
development headers installed, the probe succeeds, enabling BUILD_DISAS.
Subsequent compilation of objtool then fails:

  fatal error: 'bfd.h' file not found
    113 | #include <bfd.h>

Additionally, the probe invokes $(HOSTCC) without $(HOSTCFLAGS), ignoring
any sysroot or include flags specified for the host compiler.

Fix this by including <bfd.h> and <dis-asm.h> directly in the test snippet,
passing $(HOSTCFLAGS) so host compiler options are respected, and defining
PACKAGE="objtool" to satisfy the configuration check in <bfd.h>.

Fixes: 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
Fixes: 436326bc525d ("objtool: fix build failure due to missing libopcodes check")
Reported-by: Alice Ryhl <aliceryhl@google.com>
Assisted-by: Antigravity:Gemini-Next
Signed-off-by: Ulises Mendez Martinez <umendez@google.com>
---
 tools/objtool/Makefile | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index a4484fd22a96..4cc2e756af84 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -89,9 +89,11 @@ LIBOPCODES_LIBS := $(shell \
 		    "-lopcodes -lbfd" \
 		    "-lopcodes -lbfd -liberty" \
 		    "-lopcodes -lbfd -liberty -lz"; do \
-		echo 'extern void disassemble_init_for_target(void *);' \
-		     'int main(void) { disassemble_init_for_target(0); return 0; }' | \
-			$(HOSTCC) -xc - -o /dev/null $$libs 2>/dev/null && \
+		printf '%s\n' \
+		       '$(pound)include <bfd.h>' \
+		       '$(pound)include <dis-asm.h>' \
+		       'int main(void) { disassemble_init_for_target(0); return 0; }' | \
+			$(HOSTCC) $(HOSTCFLAGS) -DPACKAGE='"objtool"' -xc - -o /dev/null $$libs 2>/dev/null && \
 			echo "$$libs" && break; \
 	done)
 
-- 
2.55.0.979.g7e5102b832-goog