go-llvm: use context-aware LLVM C APIs for functions deprecated in LLVM 22

[deadprogram]

LLVM 22 deprecated 8 global-context C API functions in favor of their
context-aware counterparts. Instead of suppressing the warnings, call
the non-deprecated InContext APIs directly.

The non-context Go functions (MDKindID, StructType, ConstString,
ConstStruct, AddBasicBlock, InsertBasicBlock) now delegate to
GlobalContext().(), which already calls the InContext C APIs.
IntPtrType calls LLVMIntPtrTypeInContext directly.

Only LLVMGetGlobalContext still needs a warning-suppression wrapper
in deprecated.c since it has no non-deprecated replacement.

The context-aware C APIs have been available since well before LLVM 14,
so this works across all supported LLVM versions.

Here is an example:

# tinygo.org/x/go-llvm
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMIntPtrType’:
cgo-gcc-prolog:477:2: warning: ‘LLVMIntPtrType’ is deprecated [-Wdeprecated-declarations]
In file included from ../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:18,
                 from ../../../go/pkg/mod/tinygo.org/x/go-llvm@v0.0.0-20260707200325-ddd595b68360/target.go:16:
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Target.h:234:41: note: declared here
  234 | LLVM_ATTRIBUTE_C_DEPRECATED(LLVMTypeRef LLVMIntPtrType(LLVMTargetDataRef TD),
      |                                         ^~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
# tinygo.org/x/go-llvm
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMAppendBasicBlock’:
cgo-gcc-prolog:285:2: warning: ‘LLVMAppendBasicBlock’ is deprecated [-Wdeprecated-declarations]
In file included from ../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:18,
                 from ../../../go/pkg/mod/tinygo.org/x/go-llvm@v0.0.0-20260707200325-ddd595b68360/ir.go:16:
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:3717:23: note: declared here
 3717 |     LLVMBasicBlockRef LLVMAppendBasicBlock(LLVMValueRef Fn, const char *Name),
      |                       ^~~~~~~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMConstString’:
cgo-gcc-prolog:2925:2: warning: ‘LLVMConstString’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:2489:18: note: declared here
 2489 |     LLVMValueRef LLVMConstString(const char *Str, unsigned Length,
      |                  ^~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMConstStruct’:
cgo-gcc-prolog:2966:2: warning: ‘LLVMConstStruct’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:2538:18: note: declared here
 2538 |     LLVMValueRef LLVMConstStruct(LLVMValueRef *ConstantVals, unsigned Count,
      |                  ^~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMGetGlobalContext’:
cgo-gcc-prolog:4229:2: warning: ‘LLVMGetGlobalContext’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:593:44: note: declared here
  593 | LLVM_ATTRIBUTE_C_DEPRECATED(LLVMContextRef LLVMGetGlobalContext(void),
      |                                            ^~~~~~~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMGetMDKindID’:
cgo-gcc-prolog:4597:2: warning: ‘LLVMGetMDKindID’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:669:14: note: declared here
  669 |     unsigned LLVMGetMDKindID(const char *Name, unsigned SLen),
      |              ^~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMInsertBasicBlock’:
cgo-gcc-prolog:5664:2: warning: ‘LLVMInsertBasicBlock’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:3739:23: note: declared here
 3739 |     LLVMBasicBlockRef LLVMInsertBasicBlock(LLVMBasicBlockRef InsertBeforeBB,
      |                       ^~~~~~~~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
cgo-gcc-prolog: In function ‘_cgo_2ad2ad839789_Cfunc_LLVMStructType’:
cgo-gcc-prolog:8039:2: warning: ‘LLVMStructType’ is deprecated [-Wdeprecated-declarations]
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Core.h:1580:17: note: declared here
 1580 |     LLVMTypeRef LLVMStructType(LLVMTypeRef *ElementTypes, unsigned ElementCount,
      |                 ^~~~~~~~~~~~~~
../../../work/tinygo/tinygo/llvm-project/llvm/include/llvm-c/Deprecated.h:29:3: note: in definition of macro ‘LLVM_ATTRIBUTE_C_DEPRECATED’
   29 |   decl __attribute__((deprecated))
      |   ^~~~
ok  	github.com/tinygo-org/tinygo/builder	48.021s

[deadprogram]

Updated this PR to actually call the context-aware functions, not just surpress the warnings.

[dgryski]

LGTM

[deadprogram]

Thank you for the quick review @dgryski now merging.