clang prefix for centos7

I'm migating a postgres11 server to centos7.
It turns out we need parray_gin extension.

Under centos6, it compiled and installed fine, but but under c7 it fails:

sudo pgxnclient install parray_gin
|INFO: best version: parray_gin 1.3.1
|INFO: saving /tmp/tmpyrOi8w/parray_gin-1.3.1.zip
|INFO: unpacking: /tmp/tmpyrOi8w/parray_gin-1.3.1.zip
|INFO: building extension
|gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -I. -I./ -I/usr/pgsql-11/include/server -I/usr/pgsql-11/include/internal -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include -c -o src/parray_gin.o src/parray_gin.c
|gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -I. -I./ -I/usr/pgsql-11/include/server -I/usr/pgsql-11/include/internal -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include -c -o src/trgm.o src/trgm.c
|gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -shared -o parray_gin.so src/parray_gin.o src/trgm.o -L/usr/pgsql-11/lib -Wl,--as-needed -L/usr/lib64/llvm5.0/lib -L/usr/lib64 -Wl,--as-needed -Wl,-rpath,'/usr/pgsql-11/lib',--enable-new-dtags
|cp sql/parray_gin.sql sql/parray_gin--1.3.1.sql
|/opt/rh/llvm-toolset-7/root/usr/bin/clang -Wno-ignored-attributes -fno-strict-aliasing -fwrapv -O2 -I. -I./ -I/usr/pgsql-11/include/server -I/usr/pgsql-11/include/internal -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include -flto=thin -emit-llvm -c -o src/parray_gin.bc src/parray_gin.c
|gmake: /opt/rh/llvm-toolset-7/root/usr/bin/clang: Command not found
|gmake: *** [src/parray_gin.bc] Error 127
|ERROR: command returned 2: gmake PG_CONFIG=/bin/pg_config all

I guess that's because of:
[pryzbyj(at)database parray_gin-1.3.1]$ /usr/pgsql-11/bin/pg_config
CONFIGURE = ... 'CLANG=/opt/rh/llvm-toolset-7/root/usr/bin/clang' ...

Searching for "/opt/rh/llvm-toolset-7/root/usr/bin/clang: Command not found", I
see it's affected a bunch of people and a bunch of different extensions.

Is it possible to compile with CLANG=/usr/bin/clang, instead ?

Thanks,
Justin