libllvmminimal: Add missing Support/ABIBreak.cpp

[jrtc27]

Summary

When building natively on RISC-V, linking the bootstrap clang-tblgen
fails with:

ld: error: undefined symbol: llvm::EnableABIBreakingChecks
>>> referenced by PrettyStackTrace.cpp
>>>               PrettyStackTrace.o:(.sdata+0x0) in archive
/usr/obj/usr/src/freebsd-src/riscv.riscv64/tmp/obj-tools/lib/clang/libllvmminimal/libllvmminimal.a
>>> referenced by Signals.cpp
>>>               Signals.o:(.sdata+0x8) in archive
/usr/obj/usr/src/freebsd-src/riscv.riscv64/tmp/obj-tools/lib/clang/libllvmminimal/libllvmminimal.a
>>> referenced by Timer.cpp
>>>               Timer.o:(.sdata+0x28) in archive
/usr/obj/usr/src/freebsd-src/riscv.riscv64/tmp/obj-tools/lib/clang/libllvmminimal/libllvmminimal.a

This is likely due to Error.h's inclusion of abi-breaking.h. It's
unclear why this only affects RISC-V, but perhaps relates to its more
eager use of .sdata due to the ABI's support for linker relaxations.
Regardless, this is theoretically an issue for all architectures.

Reported by: Dennis Clarke <[e-mail]>

Test Plan

Have pinged Dennis to see if he can verify that buildworld now succeeds (or at
least gets further).

[dim]

Sure, this is fine. Please mark it for MFC too.

[dclarke_blastwave.org]

This change does allow me to get paste this little hiccup and then we run into a problem with -Wl,--gc-sections in lib/clang/llvm.build.mk so the trivial hack is to comment out that line and continue. Which seems to work thus far however I suspect this buildworld will run for days.

ijiraq# 
ijiraq# uname -apKU
FreeBSD ijiraq 13.0-ALPHA1 FreeBSD 13.0-ALPHA1 #0 main-c256037-gf3ea417f96b0: Sun Jan 17 21:27:09 GMT 2021     root@ijiraq:/usr/obj/usr/src/freebsd-src/riscv.riscv64/sys/GENERIC  riscv riscv64 1300136 1300133
ijiraq# diff -u llvm.build.mk.orig /usr/src/freebsd-src/lib/clang/llvm.build.mk
--- llvm.build.mk.orig  2021-01-27 22:39:50.714882000 +0000
+++ /usr/src/freebsd-src/lib/clang/llvm.build.mk        2021-01-29 21:50:32.329284000 +0000
@@ -100,7 +100,7 @@
 
 CFLAGS+=       -ffunction-sections
 CFLAGS+=       -fdata-sections
-LDFLAGS+=      -Wl,--gc-sections
+# LDFLAGS+=    -Wl,--gc-sections
 
 CXXSTD?=       c++14
 CXXFLAGS+=     -fno-exceptions
ijiraq#

[dclarke_blastwave.org]

Happy to report that native buildworld did eventually complete just fine.

ijiraq# uname -apKU 
FreeBSD ijiraq 13.0-ALPHA1 FreeBSD 13.0-ALPHA1 #0 main-c256037-gf3ea417f96b0: Sun Jan 17 21:27:09 GMT 2021     root@ijiraq:/usr/obj/usr/src/freebsd-src/riscv.riscv64/sys/GENERIC  riscv riscv64 1300136 1400002
ijiraq#

[dclarke_blastwave.org]

Currently re-running buildworld to confirm.