Update go_library build rule to compile assembly files individually (#330)

Currently, when compiling a Go package with Assembly files, the
`go_library` build rule invokes `go tool asm` once on all Assembly files
in the package. However, this caused errors that look like the below
when multiple files declare symbols with the same name.

```
asm: pkg/linux_amd64/github.com/apache/arrow-go/v18/internal/utils/min_max_sse4_amd64.s:8: symbol LCDATA1 redeclared
asm: pkg/linux_amd64/github.com/apache/arrow-go/v18/internal/utils/min_max_sse4_amd64.s:242: symbol LCDATA2 redeclared
asm: pkg/linux_amd64/github.com/apache/arrow-go/v18/internal/utils/min_max_sse4_amd64.s:460: symbol LCDATA3 redeclared
asm: pkg/linux_amd64/github.com/apache/arrow-go/v18/internal/utils/min_max_sse4_amd64.s:691: symbol LCDATA4 redeclared
asm: pkg/linux_amd64/github.com/apache/arrow-go/v18/internal/utils/min_max_sse4_amd64.s:847: symbol LCDATA5 redeclared
asm: assembly failed
```

This is despite the `<>` suffix [1] after the offending symbol name,
which should've been enough to make the symbol visible in that file
only [2] from the perspective of `go tool asm`.

When building this same package without Please (i.e. just with
`go build`), we don't run into these errors - it looks like this is
because the Go tool invokes `go tool asm` on each Assembly
individually [3, 4]. So this PR updates the `go_library` build def's
behaviour to more closely match the behaviour in the Go tool.

I was able to reproduce these errors by adding the new unit tests in
this PR. The errors were fixed by my updates to the `go_library` build
def.

[1] https://github.com/apache/arrow-go/blob/main/internal/utils/min_max_sse4_amd64.s#L8
[2] https://go.dev/doc/asm#:~:text=Adding%20%3C%3E%20to%20the%20name%2C%20as%20in%20foo%3C%3E(SB)%2C%20makes%20the%20name%20visible%20only%20in%20the%20current%20source%20file%2C%20like%20a%20top%2Dlevel%20static%20declaration%20in%20a%20C%20file
[3] https://cs.opensource.google/go/go/+/master:src/cmd/go/internal/work/gccgo.go;l=212
[4] https://cs.opensource.google/go/go/+/master:src/cmd/go/internal/work/gc.go;l=397

Co-authored-by: Chris Novakovic <chris@chrisn.me.uk>

Author: kelvinjhwong

build_defs/go.build_defs

@@ -424,9 +424,22 @@ def go_library(name:str, srcs:list, resources:list=[], asm_srcs:list=None, hdrs:
                 'hdrs': [hdrs_rule],
                 'goasm': [lib_rule + '|h'],
             },
-            outs = [name + '.o'],
+            outs = [name + "#" + (splitext(basename(a)))[0] + ".o" for a in asm_srcs],
             building_description = 'Assembling...',
-            cmd = f'eval `"$TOOL" env` && mkdir include && mv $SRCS_GOASM include/go_asm.h && "$TOOL" tool asm -trimpath "$TMP_DIR" -I "$TMP_DIR"/include -I ${GOROOT}/pkg/include -D GOOS={CONFIG.OS} -D GOARCH_{CONFIG.ARCH} -p {package_path} -o "$OUT" $SRCS_ASM',
+            cmd = " && ".join([
+                'eval `"$TOOL" env`',
+                'mkdir include',
+                'mv $SRCS_GOASM include/go_asm.h',
+                'for ASM_FILE in $SRCS_ASM; do "$TOOL" tool asm ' + " ".join([
+                    '-trimpath "$TMP_DIR"',
+                    '-I "$TMP_DIR"/include',
+                    '-I ${GOROOT}/pkg/include',
+                    f'-D GOOS={CONFIG.OS}',
+                    f'-D GOARCH_{CONFIG.ARCH}',
+                    f'-p {package_path}',
+                    f'''-o "{name}#$(basename $ASM_FILE | sed -e 's/\.[sS]$//').o"''',
+                ]) + ' $ASM_FILE; done',
+            ]),
             env= {
                 "GOOS": CONFIG.OS,
                 "GOARCH": CONFIG.ARCH,

test/asm/lib/BUILD

@@ -3,7 +3,10 @@ subinclude("//build_defs:go")
 go_library(
     name = "asm",
     srcs = ["asm.go"],
-    asm_srcs = ["add.s"],
+    asm_srcs = [
+        "add.s",
+        "subtract.s",
+    ],
     deps = ["//test/asm/lib/golib"],
 )
 

test/asm/lib/add.s

@@ -1,3 +1,5 @@
+GLOBL COLLIDINGSYMBOL<>(SB), 8, $32
+
 // func add(x, y int64)
 TEXT ·add(SB),$0-24
     MOVQ x+0(FP), BX

test/asm/lib/asm.go

@@ -10,3 +10,11 @@ func add(x, y int64) int64
 func Add() int {
 	return int(add(golib.LHS, golib.RHS))
 }
+
+// subtract is the forward declaration of the assembly implementation.
+func subtract(x, y int) int64
+
+// Subtract subtracts two numbers using assembly.
+func Subtract() int {
+	return int(subtract(golib.LHS, golib.RHS))
+}

test/asm/lib/asm_test.go

@@ -11,5 +11,9 @@ import (
 )
 
 func TestAssemblyAdd(t *testing.T) {
-	assert.Equal(t, 15, asm.Add())
+	assert.Equal(t, 14, asm.Add())
+}
+
+func TestAssemblySubtract(t *testing.T) {
+	assert.Equal(t, 6, asm.Subtract())
 }

test/asm/lib/golib/go_lib.go

@@ -1,4 +1,4 @@
 package golib
 
-const LHS = 5
-const RHS = 10
+const LHS = 10
+const RHS = 4

test/asm/lib/subtract.s

@@ -0,0 +1,9 @@
+GLOBL COLLIDINGSYMBOL<>(SB), 8, $32
+
+// func subtract(x, y int64)
+TEXT ·subtract(SB),$0-24
+    MOVQ x+0(FP), BX
+	MOVQ y+8(FP), BP
+    SUBQ BP, BX
+    MOVQ BX, ret+16(FP)
+    RET