Implicit make rules break test examples

Hi,

In src/test/example, the implicit make rules produce errors:

make -C ../../../src/backend generated-headers
make[1]: Entering directory '/home/ddong/postgresql/bld/src/backend'
make -C catalog distprep generated-header-symlinks
make[2]: Entering directory '/home/ddong/postgresql/bld/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 '/home/ddong/postgresql/bld/src/backend/catalog'
make -C utils distprep generated-header-symlinks
make[2]: Entering directory '/home/ddong/postgresql/bld/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 '/home/ddong/postgresql/bld/src/backend/utils'
make[1]: Leaving directory '/home/ddong/postgresql/bld/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
-I/home/ddong/postgresql/bld/../src/interfaces/libpq
-I../../../src/include -I/home/ddong/postgresql/bld/../src/include
-D_GNU_SOURCE -c -o testlibpq.o
/home/ddong/postgresql/bld/../src/test/examples/testlibpq.c
gcc -L../../../src/port -L../../../src/common -L../../../src/common
-lpgcommon -L../../../src/port -lpgport
-L../../../src/interfaces/libpq -lpq -Wl,--as-needed
-Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags testlibpq.o -o
testlibpq
testlibpq.o: In function `exit_nicely':
testlibpq.c:(.text.unlikely+0x5): undefined reference to `PQfinish'
testlibpq.o: In function `main':
testlibpq.c:(.text.startup+0x22): undefined reference to `PQconnectdb'
testlibpq.c:(.text.startup+0x2d): undefined reference to `PQstatus'
testlibpq.c:(.text.startup+0x44): undefined reference to `PQexec’
…

I think the -lpq flag does not have any effects in the middle of the
arguments. It works if move the flag to the end:

gcc -L../../../src/port -L../../../src/common -L../../../src/common
-lpgcommon -L../../../src/port -lpgport
-L../../../src/interfaces/libpq -Wl,--as-needed
-Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags testlibpq.o -o
testlibpq -lpq

So I added an explicit rule to rearrange the flags:

gcc testlibpq.o -o testlibpq -L../../../src/port -L../../../src/common
-L../../../src/common -lpgcommon -L../../../src/port -lpgport
-L../../../src/interfaces/libpq -lpq -Wl,--as-needed
-Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags

Then the make command works as expected. This is my first time writing
a patch. Please let me know what you think!

Thank you,
Happy new year!
Donald Dong