Well, not sure if we're having the same issue here but on my side, it fails here :
gcc -O3 -Wall -Wextra -Wundef -Wcast-qual -Wcast-align -Wshadow -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wpointer-arith -Wstrict-aliasing=1 -I../lib -DXXH_NAMESPACE=LZ4_ -c -o datagen.o datagen.c
gcc -O3 -Wall -Wextra -Wundef -Wcast-qual -Wcast-align -Wshadow -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wpointer-arith -Wstrict-aliasing=1 -I../lib -DXXH_NAMESPACE=LZ4_ -c -o lz4cli.o lz4cli.c
gcc -O3 -Wall -Wextra -Wundef -Wcast-qual -Wcast-align -Wshadow -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wpointer-arith -Wstrict-aliasing=1 -I../lib -DXXH_NAMESPACE=LZ4_ -c -o lz4io.o lz4io.c
Undefined first referenced
symbol in file
nanosleep bench.o
ld: fatal: symbol referencing errors. No output written to lz4
gmake[1]: *** [lz4] Error 1
gmake: *** [lz4] Error 2
gmake: *** Waiting for unfinished jobs....
gcc -O3 -Wall -Wextra -Wundef -Wcast-qual -Wcast-align -Wshadow -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wpointer-arith -Wstrict-aliasing=1 -I../lib -DXXH_NAMESPACE=LZ4_ -Wl,-R/srv/pbulk/lib ../lib/lz4.o ../lib/lz4frame.o ../lib/lz4hc.o ../lib/xxhash.o bench.o datagen.o lz4cli.o lz4io.o -o lz4
gmake[1]: Leaving directory `/var/tmp/pbulkbuild/archivers/lz4/work/lz4-1.9.2/programs'
creating versioned links
gmake[1]: Leaving directory `/var/tmp/pbulkbuild/archivers/lz4/work/lz4-1.9.2/lib'
*** Error code 2
Stop.
bmake[3]: stopped in /srv/pkgsrc/archivers/lz4
*** Error code 1
Stop.
bmake[2]: stopped in /srv/pkgsrc/archivers/lz4
*** Error code 1
Stop.
bmake[1]: stopped in /srv/pkgsrc/net/rsync
*** Error code 1
Stop.
bmake: stopped in /srv/pkgsrc/pkgtools/pbulk
My PATH is "/usr/sbin:/usr/bin:/opt/csw/bin:/usr/sfw/bin:/usr/pkg/bin:/usr/pkg/sbin:/usr/ccs/bin:/usr/local/bin:/usr/local/sbin"
As I previously said, it fails ONLY with pkgsrc2020Q3.
pkgsrc2020Q2 bootstrap (and works) fine.