build: Retire LLVM_COV src.conf knob

I introduced it in commit 1b49115a40 ("Promote llvm-cov to a
standalone option").  llvm-cov was previously enabled as part of the
CLANG_EXTRAS option.  I made it a standalone, default-enabled option for
parity with the tools provided by the GCC-based toolchain.

We no longer provide an in-tree GCC toolchain.  Now, just build llvm-cov
along with Clang to simplify build infrastructure.

Reviewed by:	dim
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D58155

lib/clang/libllvm/Makefile

@@ -2205,10 +2205,9 @@ SRCS_ALL+=	${SRCS_XDL}
 .if ${MK_CLANG_EXTRAS} != "no" || ${MK_LLDB} != "no" || !defined(TOOLS_PREFIX)
 SRCS_ALL+=	${SRCS_XDW}
 .endif
-.if ${MK_LLVM_COV} != "no"
+# LLVM_COV retired, just part of Clang now
 SRCS_ALL+=	${SRCS_COV}
-.endif
-.if ${MK_LLVM_COV} != "no" || ${MK_LLD} != "no" || \
+.if ${MK_LLD} != "no" || \
     (defined(TOOLS_PREFIX) && ${MK_LLD_BOOTSTRAP} != "no")
 SRCS_ALL+=	${SRCS_COL}
 .endif

share/man/man5/src.conf.5

@@ -1,5 +1,5 @@
 .\" DO NOT EDIT-- this file is @generated by tools/build/options/makeman.
-.Dd July  9, 2026
+.Dd July 10, 2026
 .Dt SRC.CONF 5
 .Os
 .Sh NAME
@@ -397,8 +397,6 @@ When set, it enforces these options:
 .Va WITHOUT_CLANG_FORMAT
 .It
 .Va WITHOUT_CLANG_FULL
-.It
-.Va WITHOUT_LLVM_COV
 .El
 .Pp
 When set, these options are also in effect:
@@ -993,10 +991,6 @@ To be able to build the system alternate binary utilities must be provided via
 and
 .Ev XSTRIPBIN .
 
-.It Va WITHOUT_LLVM_COV
-Do not build the
-.Xr llvm-cov 1
-tool.
 .It Va WITH_LLVM_FULL_DEBUGINFO
 Generate full debug information for LLVM libraries and tools, which uses
 more disk space and build resources, but allows for easier debugging.
@@ -1841,8 +1835,6 @@ When set, it enforces these options:
 .Va WITHOUT_LLD
 .It
 .Va WITHOUT_LLDB
-.It
-.Va WITHOUT_LLVM_COV
 .El
 .Pp
 When set, these options are also in effect:

share/mk/src.opts.mk

@@ -124,7 +124,6 @@ __DEFAULT_YES_OPTIONS = \
     LLVM_ASSERTIONS \
     LLVM_BINUTILS \
     LLVM_BINUTILS_BOOTSTRAP \
-    LLVM_COV \
     LOADER_BIOS \
     LOADER_BIOS_TEXTONLY \
     LOADER_GELI \
@@ -511,7 +510,6 @@ MK_LLVM_BINUTILS:=	no
 MK_CLANG_EXTRAS:= no
 MK_CLANG_FORMAT:= no
 MK_CLANG_FULL:= no
-MK_LLVM_COV:= no
 .endif
 
 .if ${MK_ASAN} == "yes"

tools/build/mk/OptionalObsoleteFiles.inc

@@ -895,7 +895,7 @@ OLD_LIBS+=usr/lib/libprivateclang.so.21
 .endif
 
 .if (${MK_CLANG_EXTRAS} == no && ${MK_CLANG} == no && ${MK_LLDB} == no && \
-    ${MK_LLD} == no && ${MK_LLVM_BINUTILS} == no && ${MK_LLVM_COV} == no) || \
+    ${MK_LLD} == no && ${MK_LLVM_BINUTILS} == no) || \
     ${MK_LLVM_LINK_STATIC_LIBRARIES} != no
 OLD_LIBS+=usr/lib/libprivatellvm.so.21
 .endif
@@ -3925,7 +3925,7 @@ OLD_FILES+=usr/share/man/man1/lldb-server.1.gz
 OLD_FILES+=usr/share/man/man1/lldb.1.gz
 .endif
 
-.if ${MK_LLVM_COV} == no
+.if ${MK_CLANG} == no
 OLD_FILES+=usr/bin/gcov
 OLD_FILES+=usr/bin/llvm-cov
 OLD_FILES+=usr/bin/llvm-profdata

tools/build/options/WITHOUT_LLVM_COV

@@ -1,3 +0,0 @@
-Do not build the
-.Xr llvm-cov 1
-tool.

tools/build/options/WITH_LLVM_COV

@@ -1,3 +0,0 @@
-Build the
-.Xr llvm-cov 1
-tool.

usr.bin/clang/Makefile

@@ -62,7 +62,7 @@ SUBDIR+=	lld
 SUBDIR+=	lldb
 SUBDIR+=	lldb-server
 .endif
-.if ${MK_LLVM_COV} != "no"
+.if ${MK_CLANG} != "no"
 SUBDIR+=	llvm-cov
 SUBDIR+=	llvm-profdata
 SUBDIR_DEPEND_toolchain=	llvm-cov

usr.bin/clang/toolchain/Makefile

@@ -7,10 +7,8 @@ SYMLINKS+=	llvm-ar ${BINDIR}/ar
 SYMLINKS+=	llvm-ranlib ${BINDIR}/ranlib
 MLINKS+=	llvm-ar.1 ar.1 llvm-ar.1 ranlib.1
 
-.if ${MK_LLVM_COV} != "no"
 SYMLINKS+=	llvm-cov ${BINDIR}/gcov
 MLINKS=		llvm-cov.1 gcov.1
-.endif
 
 SYMLINKS+=	llvm-cxxfilt ${BINDIR}/c++filt
 MLINKS+=	llvm-cxxfilt.1 c++filt.1