build issue with PostgreSQL 12

[githubgrscporg]

System is Ubuntu Linux, 18.04, both postgresql and pgsphere built from source
pgsphere is unzip'd to postgresql-12.0/contrib/pgsphere-master

"make" results in:

rm -f pg_sphere.so libpg_sphere.a libpg_sphere.pc
rm -f pg_sphere--1.0.sql
rm -f sscan.o sparse.o sbuffer.o vector3d.o point.o euler.o circle.o line.o ellipse.o polygon.o path.o box.o output.o gq_cache.o gist.o key.o gnomo.o sscan.bc sparse.bc sbuffer.bc vector3d.bc point.bc euler.bc circle.bc line.bc ellipse.bc polygon.bc path.bc box.bc output.bc gq_cache.bc gist.bc key.bc gnomo.bc
rm -rf pg_sphere--1.0.sql pgs_types.sql pgs_point.sql pgs_euler.sql pgs_circle.sql pgs_line.sql pgs_ellipse.sql pgs_polygon.sql pgs_path.sql pgs_box.sql pgs_contains_ops.sql pgs_contains_ops_compat.sql pgs_gist.sql gnomo.sql
rm -rf results/ regression.diffs regression.out tmp_check/ tmp_check_iso/ log/ output_iso/
make -C ../../src/backend generated-headers
make[1]: Entering directory '/scratch0/local/src/postgresql-12.0/src/backend'
make -C catalog distprep generated-header-symlinks
make[2]: Entering directory '/scratch0/local/src/postgresql-12.0/src/backend/catalog'
make[2]: Nothing to be done for 'distprep'.
make[2]: Nothing to be done for 'generated-header-symlinks'.
make[2]: Leaving directory '/scratch0/local/src/postgresql-12.0/src/backend/catalog'
make -C utils distprep generated-header-symlinks
make[2]: Entering directory '/scratch0/local/src/postgresql-12.0/src/backend/utils'
make[2]: Nothing to be done for 'distprep'.
make[2]: Nothing to be done for 'generated-header-symlinks'.
make[2]: Leaving directory '/scratch0/local/src/postgresql-12.0/src/backend/utils'
make[1]: Leaving directory '/scratch0/local/src/postgresql-12.0/src/backend'
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o sscan.o sscan.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o sparse.o sparse.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o sbuffer.o sbuffer.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o vector3d.o vector3d.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o point.o point.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o euler.o euler.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o circle.o circle.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o line.o line.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o ellipse.o ellipse.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2 -fPIC -I. -I. -I../../src/include -D_GNU_SOURCE -c -o polygon.o polygon.c
polygon.c: In function ‘spherepoly_in’:
polygon.c:827:3: error: ISO C90 forbids variable length array ‘arr’ [-Werror=vla]
SPoint arr[nelem];
^~~~~~
polygon.c: In function ‘spherepoly_area’:
polygon.c:895:2: error: ISO C90 forbids variable length array ‘s’ [-Werror=vla]
SPoint s[poly->npts + 2];
^~~~~~
cc1: some warnings being treated as errors
: recipe for target 'polygon.o' failed
make: *** [polygon.o] Error 1

I am not a C programmer, and I was unable to successfully modify the pgsphere code, nor was I successful in using c99 rather then gcc as the compiler (a suggestion found while searching the above errors). But I was able to get this to build making the following change in postgresql-12.0/src/Makefile.global:

--- Makefile.global.original 2019-10-28 15:44:22.976557899 -0700
+++ Makefile.global 2019-10-28 16:46:10.969861000 -0700
@@ -257,7 +257,7 @@
GCC = yes
SUN_STUDIO_CC = no
CXX = g++
-CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2
+CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2
CFLAGS_VECTOR = -funroll-loops -ftree-vectorize
CFLAGS_SSE42 = -msse4.2
CFLAGS_ARMV8_CRC32C =