Using -g for non-macho targets can cause driver planning errors

[rauhul]

Building a binary for -target armv7em-none-none-eabi with -o and -emit-module works if -g is not specified.

Works:

➜  Desktop xcrun --toolchain org.swift.59202403131a swiftc -target armv7em-none-none-eabi -c foo.swift -o foo.o -emit-module -wmo -enable-experimental-feature Embedded

Fails:

➜  Desktop xcrun --toolchain org.swift.59202403131a swiftc -target armv7em-none-none-eabi -c foo.swift -o foo.o -emit-module -wmo -enable-experimental-feature Embedded -g
SwiftDriverExecution/MultiJobExecutor.swift:207: Fatal error: multiple producers for output foo.o: Wrapping Swift module foo & Compiling foo foo.swift
[1]    85772 trace trap  xcrun --toolchain org.swift.59202403131a swiftc -target armv7em-none-none-eab

Failing Frontend commands:

/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/bin/swift-frontend -frontend -c foo.swift -target armv7em-none-none-eabi -disable-objc-interop -sdk /Applications/XcodeGeode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk -color-diagnostics -g -debug-info-format=dwarf -dwarf-version=4 -enable-experimental-feature Embedded -empty-abi-descriptor -resource-dir /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/rauhul/Desktop -module-name foo -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/local/lib/swift/host/plugins -o foo.o
/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/bin/swift-frontend -frontend -emit-module -experimental-skip-non-inlinable-function-bodies-without-types foo.swift -target armv7em-none-none-eabi -disable-objc-interop -sdk /Applications/XcodeGeode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk -color-diagnostics -g -debug-info-format=dwarf -dwarf-version=4 -enable-experimental-feature Embedded -empty-abi-descriptor -resource-dir /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/rauhul/Desktop -module-name foo -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/local/lib/swift/host/plugins -emit-module-doc-path foo.swiftdoc -emit-module-source-info-path foo.swiftsourceinfo -o foo.swiftmodule
/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-03-13-a.xctoolchain/usr/bin/swift-frontend -modulewrap foo.swiftmodule -target armv7em-none-none-eabi -o foo.o

[hamishknight]

Also fails without -g if the -o is for the module:

❯ ./swiftc -emit-module -c ~/src/swift-test-arena/swift-test-arena/main.swift -o /tmp/main.swiftmodule
SwiftDriverExecution/MultiJobExecutor.swift:207: Fatal error: multiple producers for output /tmp/main.swiftmodule: Compiling main main.swift & Emitting module for main